This is a tricky question to ask correctly. One attempt has already been closed as subjective and argumentative. There is no one correct answer, for sure. However, there are interesting reasons that I believe are worth recording here.

Ideally include supporting documentation/research. I will vote up for quality of answer, not based on whether I agree with the answer.

locked by freiheit Feb 11 '12 at 18:16

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  • Certainly a worthwhile question, although as @Jay has noticed, one with no clear answer. Please flag any posts for moderator attention if necessary. – Neil Fein Oct 18 '10 at 0:29
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    I don't think one reason per post works well here at all. I would rebuild this question from scratch and ask people to make the most compelling case they can -- either for or against -- and cite experiences and data to back up that case. The best post here is the deleted one, sadly. :( – Jeff Atwood Oct 18 '10 at 10:51
  • @Jeff - Not an either/or situation. We can try it both ways, and keep the one that answers the question better and more comprehensively. Anyone want to take a crack at writing a version of this question that will work? (Perhaps this thread can be used to generate bullet points for arguments pro and con for such a complete-answer thread.) – Neil Fein Oct 18 '10 at 11:49
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    I keep wondering about the odd design that cycling helmets are? They look like they would work great if you landed right on top of your head, but who does that? The people I see crash hit much lower on the head (face first), where the helmet doesn't protect. Seems like they're very poorly designed for the task. – Brian Knoblauch Oct 19 '10 at 12:23
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    @Brian - I've hit myself on the top of my head twice, and had to replace my helmet. Just because a solution doesn't address all of the problem doesn't mean it's worthless. (And there are motorcycle-style helmets you can get.) – Neil Fein Oct 19 '10 at 14:30

34 Answers 34


For: If you fall on top of your head, it will protect it (also side impacts if wearing a full-face helmet while riding downhill mountain bike)

No, this is not an overly simple reply. It's what it's designed for, it's what it does well and it's why you should wear one.

Feel free to edit with documentation about head protection, but I think the number of people on here (myself first) who can say "I fell and my helmet saved my head" are worth any research.

  • is my edit in the spirit of what you meant to write? Not trying to say helmets aren't useful, just trying to be objective. – Neil Fein Oct 18 '10 at 0:46
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    @neilfein: re-edited, keeping your edit in mind – dee-see Oct 18 '10 at 0:47
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    i agree with this whole-heartedly. Shit happens, so why not be protected. – fady Oct 18 '10 at 22:56
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    There are two types of people in the helmet debate. Those who can't understand what all the fuss is about, it's just a lid, right? And then there are those who've had an incident and realise that the helmet prevented something a lot worse. Of course, there is a third group, but they can't read these posts. – Unsliced Oct 22 '10 at 11:23

Against compulsory: where it is compulsory it discourages people from cycling -> they drive instead -> more cars+fewer cyclists make it more dangerous for cyclists.

Personally I wear one, but this is the main argument against compulsory helmet.

  • It discourages people from cycling ? Not saying it doesn't, just asking why you're saying that... people who don't want to wear a helmet cycle without one, they don't drive. – dee-see Oct 18 '10 at 23:54
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    sorry - I meant where it's COMPULSORY it discourages people from cycling. – mgb Oct 19 '10 at 3:45
  • Oh that's right. +1 – dee-see Oct 19 '10 at 16:35
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    In a fantasy world where all cars were replaced by bikes/buses/horses, would anyone wear a helmet? – Jay Bazuzi Oct 20 '10 at 15:49
  • I would - but I'm rather attached to my head! But even if they didn't, a cyclists with no helmet in a world without cars is safer than a compulsory helmet and being the only cyclist in a stream of cars. – mgb Oct 20 '10 at 16:07

Against: There has been some research that showed:

  • Car drivers tend to think that a cyclist that is wearing a helmet is a safer cyclist.
  • Car driver tend to give “safer cyclists” less space.

So by wearing a helmet you may increase the risk from car drivers not giving you enough space!

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    If you follow up on some of the links there, or actually read the research or look at the data you find that it was a very limited study. Which is totally fine and still useful, but drawing very broad conclusions from it is not a great idea. The study was done in the UK and there will be regional differences due to culture and road construction. Still a good point to bring up, but read the whole thing before changing your behavior. – Mike Two Oct 18 '10 at 15:50
  • @Mike, agreed however I don’t like the fact I have to consider the effect of my bike helmet on car drivers – that study is the only good reason I have seen for not wearing a helmet my self. I saw the some problem with bike light when I lived in Cambridge(UK), car driver gave cyclists without lights a lot more space. – Ian Oct 18 '10 at 17:02
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    I don't disagree with you, but just pointing out that location may change the results. You are based in the UK I think so the study is probably applicable to you. I'm not (although I did live there for a while) so the study might not apply to me. The author of the study makes the same conclusion. In a completely non-scientific set of personal observations I think my route in my area is a bigger factor in how much space a car gives me. Some of the roads I ride on are wide and I almost always get plenty of space. Narrow roads = no space. – Mike Two Oct 19 '10 at 14:20

For: Often your friends or family will think are you safer when you wear a helmet; wearing a helmet placates your dearest-and-nearest.


  • Wearing a helmet may benefit their health by reducing their stress.
  • You may get nagged less if you wear a helmet

It might make sense to wear a helmet if it's not a discussion one cares that passionately about either way, for these reasons.

  • This is a merge of two similar answers: this one started by Ian, as well as unsliced's answer. – Neil Fein May 19 '11 at 3:25

Against legal requirement: In many countries that have made it a legal requirement to wear a bicycle helmet, the number of people cycling has reduced. Given that the risk of death due to poor health as a result of lack of exercise is a lot greater than the risk of death due to cycling without a helmet; it never makes sense to require people to use a bicycle helmet.

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    Reducing the number of cyclists + increasing cars makes it more dangerous for other cyclists (whether they are wearing helmets or not) – mgb Oct 18 '10 at 22:02
  • This argument fails in the modern social welfare state (read: all developed countries). If you fall and injure yourself to the point of requiring long-term medical care, We are the ones that pay for it. Unless you are independently wealthy (and become forced to finance your medical expenses out-of-pocket), I would like to be able to force you to wear a helmet. – Tom Stephens Oct 26 '10 at 1:00
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    @Tom, but the state also have to pick up the greater health cost due to lack of exercise. – Ian Oct 26 '10 at 8:00

Against: It may not really be necessary. If I'm riding very casually with no vehicles, a fall would be similar in effect to falling while jogging. Both at college where we had roads closed to cars as well as riding around the farm.

Of course, this implies not riding at speeds where a failure (rider or mechanical) would cause a major problem.

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    I've seen cyclists hit each other. The fall can be pretty hard. Also, a "slow" fall on a curb or any similar object can have nasty results. – dee-see Oct 19 '10 at 16:30
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    I've seen a pedestrian fall onto the back of his head whilst negotiating a tricky piece of flat pavement. He just got up and carried on. – Tom Hawtin - tackline Oct 21 '10 at 12:35
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    I had an accident with zero speed forward, because of a full braking, but I had my feet in pedal cages, see first picture here, and slowly felt to the side, hit the ground with my head and had one week of headaches. I'm not sure a helmet would have prevented them, but I think so. Since I had my hands at the brakes, it is very different from falling as a pedestrian, who can protect himself with the hands. – user unknown May 11 '11 at 19:18

Against: helmet hair (messes up your hair)

Depends on hair style, what you use to style your hair, how much you sweat, etc...

  • Similar: I often ride in the morning, right after I get out of the shower. The helmet keeps my hair from drying as quickly. – Neil Fein Oct 18 '10 at 4:54
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    The only reasonable solution: THE HAIRMET! youtube.com/watch?v=OL0GkcO05JE – Babu Oct 18 '10 at 15:28
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    Helmet hair prompted me to shave my head. Problem solved. – meagar Oct 21 '10 at 19:57
  • It's a perfect excuse for messy hair. The argument is right, the conclusion wrong. I vote it up. :) – user unknown May 11 '11 at 19:23
  • When my hair starts to get 'helmet hair' ridges, I know it's time for a hair cut! – Skizz Sep 20 '11 at 9:00

For: Visibility. A brightly-colored helmet is more visible than a cyclist's head. (Admittedly, a cycling cap can do this job just as well as a helmet.)


Against while commuting: It is useless.

Studies have observed that in accidents killing cyclists, the injuries were such that a helmet wouldn't have saved them. Anyway the risk of a head injury in a bike accident is about 15%, which is the same in car accident and in walk accident. Who would promote wearing helmets for car drivers or pedestrians? A documented article can be found on the site of the french organization promoting urban cycling. In summary:

  • Casual bicycling is not especially dangerous.

  • What little data exists doesn't demonstrate a correlation between increased helmet use and increased cyclist safety.

  • Mandatory helmet laws decrease bicycling substantially.

  • Cycling risks are far lower than risks associated with lack of exercise.

  • In countries where more people ride bicycles, bicycling is safer.

Conclusion: helmet laws and "fear mongering" around bicycling hurt public health

  • I'm going to go ahead and say citation needed. The one you provide is completely unconvincing. It gives overall injury/death statistics, without breaking them down into helmet/no helmet. Even worse, a quote: "Moreover, 64% of killed people had several fatal injuries and could not have been saved by a helmet." So... 36% of them potentially could have been saved by a helmet? And still others were in potentially fatal accidents and were saved by helmets. Maybe there are studies supporting your claim, but that link doesn't. – Cascabel Sep 16 '11 at 3:23

Against: A lot of people get the idea that cycling is very dangerous when they get the impression that you should always wear a helmet. In fact the health benefits from cycling outweigh the risks many times over.

So by wearing a helmet and/or telling other people it is a good idea to wear a helmet you are increasing the number of people that will die (at a early age) from heart attacks etc.

  • Where does that "people who don't want to wear a helmet don't ride bikes" logic come from? Around here people who refuse to wear helmets ride without one. – dee-see Oct 21 '10 at 11:40
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    @Domsterr, I am saying that by wearing a helmet you are meking some people who don't cycle, think that the risks of cyleing are greater then they are. – Ian Oct 21 '10 at 12:07

Against: the benefits are insufficient to justify the cost (for casual/commuting)

(note: I'm completely ignoring the cost of the helmet itself, as that's a very minor factor compared to less-direct opportunity costs)

Benefit / Opportunity cost

The benefit of wearing a helmet is to partially mitigate against the risk of death or traumatic brain injury. The other benefits (visibility, attachment points, placation) are incidental. The costs are primarily messy hair, minor discomfort and inconvenience.


From what I can tell looking at the data, the odds per year of a crash that leads to death or traumatic brain injury that could be prevented by a helmet are roughly one in a million. I'm assuming going less than 15mph (24 km/h) riding safely, etc. (factoring out minors under 18, riding drunk, people going the wrong way with no lights, etc.)

Getting any kind of truly solid numbers is difficult. It's not possible to conduct a true scientific/empirical study, so the science that's out there is either purely based on studies of dummies or can't properly correct for self-selection bias (the strong possibility is that cyclists that ride safely are more likely to be wearing a helmet).

A summary of US DOT statistics put together by the IIHS shows 714 cyclist traffic deaths for 2008. 26% of them were drunk at the time, 36% were after 9pm and before 6am.

And while those numbers only include people that actually ride cycles (the population of cyclists is smaller than the total population), it also includes people that ride the wrong way, weaving across traffic, without stopping at lights/signs, drunk, with no lights, after dark. And it includes people going quite fast (where a helmet's more likely to help in case of a fall). I'm trying to make guesses on the odds for a typical transportation/commuter cyclist who is unlikely to get over 15mph.

So I'm figuring the odds of a commuter cyclist riding in a generally safe manner being killed cycling are actually lower (less likely) than being hit by lightning (1:500,000).

I can see two ways to do the math on this:

Method #1: straight time value

Of the 525,960 average minutes in a year, I spend roughly 1400 making my hair look "good" (a few minutes most mornings washing and styling my hair, plus time for a haircut every 5 or 6 weeks). So apparently I value having my hair not look messy to the tune about about 0.266% of my life. Let's factor in comfort a bit and round that up to 0.3% (one third of 1%, or about 3 thousandths). So the annualized benefit is roughly 1/1,000,000 of my life and the cost is 1/333 of my life, so the cost is about 3,000 times the benefit.

Method #2: monetary value

I'm fond of living and consider severe brain damage almost as bad as death, so I'm going to assign a value to my life of $10,000,000 (well above my expected remaining lifetime earnings). The odds seem to be about 1/1,000,000, so the benefit is $10 per year. I spend more than $10/year on my hair (shampoo, hair gel, haircuts, etc), clothes that make me comfortable, etc ($500 seems about right). I also place probably about a $50/month ($600/year) value on comfort. It's harder to place specific monetary values on my time (the primary cost), but again it seems like the cost of wearing a helmet is at least 1,000 times the benefit.

For: the cost is justified if the risk is increased or costs reduced

If I'm engaging in a riskier riding activity (going fast, anything "technical", long enough rides that I'll get tired, riding at night, riding in wet conditions, etc), the benefit of wearing a helmet increases and it's likely math like mine works out in favor of a helmet.

If the opportunity cost goes down (bald/shaved head, long ride so I'll be sweaty and need a shower afterwards anyways, rain so I'll need a hood anyways, cold so I need a hat anyways, riding home in the dark so nobody sees my messy hair afterwards), again the math works more in favor of a helmet.

If the risk is increased and the opportunity cost goes down (long sweaty ride, ride home in the dark, rainy ride), the math goes much more strongly in favor of a helmet.

  • The odds seem surprisingly low; the odds of being struck by lightning in a given year are only 1:500,000 ([lightningsafety.noaa.gov/medical.htm]) . Do you have a source for that data? – darkcanuck Oct 26 '10 at 3:47
  • What an interesting answer. – Jay Bazuzi Oct 26 '10 at 5:40
  • @darkcanuck: Count of people in the US hit by lightning and people in the US killed riding a bicycle are about the same. Odds of being hit by lightning you cite are ignoring "selection bias" for calculating odds. (if you live in an area where lightning is rare and avoid hazardous conditions you reduce your odds of being hit by lightning by at least a factor of 20.) I'll put more in the response. – freiheit Oct 26 '10 at 21:04
  • Given that the annual US odds of dying in a motor accident is 1:6500, I think the odds are grossly underestimated here. But the real problem with this approach is that you need the probability of incidents where a helmet prevents serious injury or death -- which are not likely to ever be reported. – darkcanuck Oct 27 '10 at 3:12
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    @darkcanuck: In the US in 2008, 32,000 motorists died and only 718 cyclists. www-fars.nhtsa.dot.gov. Isn't that real problem fundamentally the same with any approach to this question? There's simply no real data on helmet efficacy. – freiheit Oct 27 '10 at 16:28

For: A helmet is a great place to mount lights, a mirror, or a rear blinky.

  • A mirror? At the helmet? Can you provide an example? (one image or product page would be okay) – Denilson Sá Maia Nov 18 '10 at 11:08
  • This thread is about providing reasons for or against helmets. – Neil Fein Nov 18 '10 at 12:42
  • Denilson Sá, here's the mirror I use: amazon.com/gp/product/B0012OKAZS It takes some getting used to, but is helpful. – Mike Ruhlin May 12 '11 at 2:21

Against: In a crash with a glancing blow, a helmet increases leverage of the impact forces around your neck. A twist-around-the-neck injury is very different from a straight-on-impact injury.

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    This is generally why helmets (of all kinds) are slick on the outside, so they don't stick to surfaces and wrench the neck. It can happen, but a glancing blow is far more likely to be the cause of injury than twisting the neck. – LanceH Oct 18 '10 at 6:21
  • While there are numerous injuries that can actually be caused by wearing a seatbelt, I once heard a traffic officer claim that he has never had to unbuckle a dead person from their automobile... Think about this one. – Tom Stephens Oct 26 '10 at 1:06
  • I heard this said in the 80's about the old styrofoam helmets that had a separate lycra cover, that the styrofoam would stick to the road. But I don't think it is any longer valid. @Jay do you have any research to back this up? At the same time I have heard that the main benefits of the leather helmets over no helmet at all is that they reduce this risk. – David LeBauer Dec 10 '10 at 5:52
  • @David no I don't have any such research. – Jay Bazuzi Dec 11 '10 at 0:41
  • Helmet shells are designed to separate from the shell and prevent this kind of injury. The old golf-ball helmets may have had this issue (although styrofoam disintegrates when dragged along pavement) any modern helmet won't have this issue. – lawndartcatcher Sep 15 '11 at 12:34

For Scientific research. (I may be able to do an against or at least inconclusive as well)

  1. A review of studies: REVIEWER'S CONCLUSIONS: Helmets reduce bicycle-related head and facial injuries for bicyclists of all ages involved in all types of crashes including those involving motor vehicles. http://www.ncbi.nlm.nih.gov/pubmed/10796827

  2. A case control study: We conclude that bicycle safety helmets are highly effective in preventing head injury. Helmets are particularly important for children, since they suffer the majority of serious head injuries from bicycling accidents. http://www.ncbi.nlm.nih.gov/pubmed/2716781

  3. Another review regarding competitive cycling: The scientific evidence that bicycle helmets protect against head, brain and facial injuries has been well established by 5 well designed case-control studies. http://www.ncbi.nlm.nih.gov/pubmed/9587180

  4. A review regarding bicycle helmet legislation: Head injuries related to bicycle use are common and can be serious. They can be prevented or reduced in severity with helmet use; however, education has resulted in modest helmet use in most developed countries. http://www.ncbi.nlm.nih.gov/pubmed/16595420

These are just a few. There is a complaint present in several studies about the lack of randomized controlled trials. There are also numerous studies regarding the use of helmets by children. An issue that comes up is that it's difficult to determine whether children are using properly fitted/properly worn helmets.


For: it might be legally required.

This depends very heavily on jurisdiction and may depend on age as well. (in my jurisdiction it's required for minors under age 18 but not for adults)


For: Wearing a helmet provides a sliding layer if you crash and slide. Would much rather have my helmet slide against the pavement than my head!

(not my head)

alt text http://www.flickr.com/photos/ian_crowther/2992217413/in/photostream/


FOR helmets AGAINST focusing only on helmets

It isn't so much that there is a negative aspect to WEARING helmets, obviously they can do little to hurt and a lot to help.

The biggest problem is that the overall focus of bike safety instruction and legislation is on helmets.

We seem to think that simply slapping a helmet on ourselves or our children is enough to secure our/their safety. We neglect to teach or focus on much more relevant bike safety issues. Like funding dedicated bike lanes/roads for (sub)urban riding, or better educating drivers about cyclists on the road

Clearly, you would be much better off if you used your head instead of just covering it with styrofoam, but doing both is definitely the preferred choice.

  • Aren't the stats for dedicated bike lanes almost as hopeless as for helmets? – Tom Hawtin - tackline Oct 26 '10 at 13:36
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    Dedicated bike lanes are ones physically separated from the roadway, not just marked off. And bike roads are pedestrian/cyclist roadways that are completely disconnected from the regular road system (see: Bay Trail in SF Bay Area). I haven't seen any negative statistics relating to these two solutions. – crasic Oct 26 '10 at 18:03
  • I think teaching vehicular cycling would help more than putting in more bike lanes. +1 for pointing out that helmets aren't everything. – freiheit Oct 26 '10 at 18:49
  • That was my point, putting in bike lanes was just an example, we focus too much on helmets and not on dozens of other safety issues in cycling – crasic Oct 26 '10 at 21:40
  • I believe the BMA (British Medical Association) cite this as one of the reasons they don't support compulsory helmet use - it would deflect the bike safety issue away from what would be really useful - physical segregation of bikes from vehicles. – Skizz Sep 20 '11 at 9:05


  • Increased head protection in falls and collisions (like with that low hanging branch you don't see until too late.) Having crashed in the past, this one is enough for me.
  • Sun protection for those of us who are 'folicularly challenged'.
  • Can be stylish.
  • May be legally required as @freihiet mentioned.
  • May increase visibility as @neilfein mentioned - I add 3M reflective tape to mine.
  • In cold weather you can tape over the vents, and use the helmet to hold a skull-cap or balaclava on to increase warmth.


  • Even the ones with the best/most vents are hotter than no helmet.
  • Some (not necessarily scientific) studies and anecdotal evidence shows that cars pass cyclists in cycling specific attire, including helmets, at a closer distance than they pass cyclists in street clothes.
  • Some (not necessarily scientific) studies and anecdotal evidence shows that when protective gear is worn, the wearer tends to engage in riskier behavior. I personally ride faster and corner more aggressively, and I think I am more assertive about taking the lane.
  • Protection in a collision is only marginal, especially if it is at a high speed or with an automobile.

Just a note about that last point - I hear that one a lot, and my usual response is that by a huge margin most accidients and collisions that result in injuries sugnificant enough to require medical attention (and therfore be tracked and reported) are not collisions or accidents involving automobiles. The most common is a 'fall' - meaning you hit something in the road or path, or otherwise lost control and fell over all on your own.


For: When swooped by birds (such as magpies) in spring, it is harder for them to take away a bit of flesh.


For: A helmet is unlikely to help you if you hit your head very hard on an object. However it reduces the likelihood of you getting a minor head injury if you fall of your bike and hit your head, or ride into a tree branch at slow speed. Therefore wearing a helmet may save you having to spend a few hours in A&E while they check you out, you may also avoid an overnight hospital stay for observation.


Against: Time to put, take off This depends on your point of view.

Against: Inconvenient to carry when off-bike.

Against: Does nothing to stop brain detaching from skull membrane which is the most important damage to avoid (cuts are mere flesh wounds)

Against: False sense of security/moral superiority If polystrene was that good then they would make lorries and formula one cars out of the stuff. Look at a big lorry coming towards you and now imagine that a cheap bit of Chinese polystyrene is going to give you Superman-esque powers of invincibility.

Against: The Dutch and Danes do not wear them, although they do buy them for children they cycle with. Although road conditions may be different in Copenhagen, they still have fast moving automobiles.

Against: Most helmets do not fit properly I have sold several hundred helmets in my time, including more than a hundred on one day (at a trade show) hence I have experience of getting them to fit, which they can be made to do. However, most helmets that I see worn are not adjusted correctly and with one's little finger you can typically flip the lid back from being on the top of the head. With a bit more force, e.g. from the rider's mass decelerating from twenty miles an hour, the ill-fitting helmet could harm the rider, strangling them. This is particularly the case with children's helmets.

Against: Reassures mother She grew up when the car was king, she continues to trash the planet with her automobile, she has no intention of ever riding a bike again, she completely believes the FUD about helmets and has the occasional road mishap herself - sound familiar? Of course you can do as you are told - by her - after all, mum knows best, doesn't she? She actually has what psychologists call 'projection' and 'denial' on the go. There comes a time when you should tell her to take a hike, or at least a bike.

Against: Anecdotal rubbish by the helmet trusters We have all heard about so-and-so's little Johnny that would have had his head split open had he not been wearing a helmet, haven't we? You cannot argue against people and their anecdotal evidence, even if little Johnny was riding back from the pub pissed on unfamiliar roads having not been much of a cyclist in the first place. If you have not hit so much as a kerb in 20+ years then you can still be deemed irresponsible by the helmet trusters.

Against: Poor quality helmet product. Only the MET helmets have straps that are soft and lie flat on the side of one's face. Giro and Bell helmets have straps that want to dig in at a 90 degree angle, typically coupled with a buckle that can painfully pinch the skin.

For: Keeps head warm in winter a helmet can keep your head out of the cold and rain.

For: Great for off-road cycling off road with any type of bravado is a bit silly without a lid.

For: Professional road racing You need a lid to road race. Unfortunately for Wouter Weylandt in this year's Giro d'Italia his helmet did not prevent his skull cracking after a crash and he is with us no more. However, no lid, no race.


For: The benefits of wearing a helmet are low; however the cost is also low. So why not wear one?


Against: It's much colder in winter to wear a helmet with an under-helmet cap than a warm winter hat. (Of course, it's much more dangerous to bike in winter, so this argument is a bit of a moot point...)

  • I am going to buy a ski helmet for this winter. – sixtyfootersdude Oct 23 '10 at 20:21

For: When mountainbiking, you can hit and push aside branches

Against: When not cleaned properly, they get a terrible smell.

Against: Ecological impact (Power consumption, CO2, chemicals) of helmet production.

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    I even signed up to comment on the "ecological impact" part. Do you really think that recovering injured people and burying those who didn't survive an accident has positive ecological impact outweighting helmet production negative? – sharptooth Oct 18 '10 at 12:55
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    Burying has a positive impact on your ecological footprint (on the long term). I'm not quite sure for a stay in the hospital. When you don't commute on your bike being in the hospital is also good (from an ecological point of view). The trip to the hospital (by car) is very bad, but is equivalent to the trip to the bike shop to buy the helmet (with car, because you do not have a helmet yet). You normally don't save a trip to the hospital per helmet, so overall impact of helmet buying vs getting injured and being transported to the hospital comes out negative on ecological footprint. – GvS Oct 18 '10 at 13:34
  • @sharptooth: I always wear my helmet (despite the bad smell). – GvS Oct 18 '10 at 13:37
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    Great, you've just sold death to me. However it'll not be that easy to sell medical equipment, complex medications and other stuff needed to heavily injured people (and stuff, alcohol and compulsive shopping included, used to relieve stress of their relatives) as "reducing ecological footprint". – sharptooth Oct 18 '10 at 14:14
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    The original question asked for one reason per answer. If we stick to the format the question proposed (and it's by no means clear how we should proceed), this should be split up into three answers. – Neil Fein Oct 18 '10 at 14:51

For: Statistics - Bicyclist deaths by helmet use, 1998-2008

"Ninety-one percent of bicyclists killed in 2008 reportedly weren't wearing helmets" http://www.iihs.org/research/fatality_facts_2008/bicycles.html

Note - This statistic was provided to me in a handout at a workplace safety and first aid workshop conducted by the Red Cross. Cycling was included in the safety section because the company has a considerable number of bike commuters. Both the company and the Red Cross promote helmet usage based on this and similar statistics.

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    Statistics aren't easy. If 92% of all riders don't wear helmets, does that mean that helmets are more likely to get you killed? – Jay Bazuzi Oct 18 '10 at 18:59
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    I don't know. In the question you stipulated one reason per post. Statistics are one reason often cited. In the real world I watched a helmeted friend smack his head into the pavement in a slow speed crash. He got a nice dent in the Giro. Since I didn't have to call 911, I figure it at least somewhat validates the statistics. – user313 Oct 18 '10 at 19:11
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    Taking a look at the Wikipedia article on bicycle helmets I ran into this quote: "...the evidence currently available is complex and full of contradictions, providing at least as much support for those who are sceptical as for those who swear by them." and this:"No randomized controlled trials have been done on the subject. The evidence comes from two main types of observational study" – user313 Oct 18 '10 at 19:25
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    Looks like someone needs to do some randomized controlled trials with crash dummies. – user313 Oct 18 '10 at 19:26
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    @wdypdx22, dummies will not tell us enough, as both the behavoir of the cyclist and of drivers change when helmet are used. Also no one know the type of accidents to test the dummies with. It is a lot more complex then a head on car crash. – Ian Oct 18 '10 at 21:36

Against: Sunburn on your forehead in strange patterns, potentially painful if your helmet sloshes around a bit. (Sunburn on your entire head in lines if you're bald.)
For: Less total sunburn on your head.

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    This is one of the worst things about loosing your hair! The sunburn lines from the helmet! But better than an entire burned head so -1! – geoffc Oct 18 '10 at 10:41
  • @geoffc - Why the downvote if you think the information is good? – Neil Fein Oct 18 '10 at 12:05
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    @neilfein: Because it is a terrible reason NOT to wear a helmet. I.e. I think it is a bad 'against'. – geoffc Oct 19 '10 at 10:44
  • @geoffc - It depends on how painful sunburn can get for you. – Neil Fein Oct 19 '10 at 13:27
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    It's a community wiki, so I edited to make sunburn both a for and an against. :) – freiheit Oct 27 '10 at 23:18

For: You will usually cycle along the road, close to the kerb. When you fall off, you are likely to fall into the kerb on your head. It happend to a friend of mine, and his helmet was dented. If he didn't wear helmet, it would have been his head.

  • Do you have an research that indicates that you'll usually hit the kerb in this scenario? Or just the single anecdote? Why did he fall? – Jay Bazuzi Oct 30 '10 at 1:51
  • Don't cycle so close to the kerb... – Tom Hawtin - tackline Nov 1 '10 at 2:42

Against: You'll live longer whether or not you wear a helmet
(insisting that one needs to wear a helmet every time I step on a bike decreases overall life expectancy since it will result in less riding)

Using myself as an example: Cycling is the bulk of the exercise I get, and I probably have a genetic predisposition to heart problems. The odds of a heart attack (or other life-threatening health problem exacerbated by lack of exercise) if I don't cycle are probably much higher than the odds of getting killed not wearing a helmet while cycling. If I felt I had to wear a helmet absolutely every time I got on a bicycle, I'd cycle less and actually reduce my life expectancy.

From what I've seen of the statistics (may have to dig up the per-passenger-mile stats stuff sometime) of death per mile of cycling are lower than per mile of being in a car or per mile of walking.

In other words: the purpose of a helmet is increasing my likely life span, and requiring or over-emphasizing helmets may work contrary to that purpose.

(Much like another response I made here, if the cycling is particularly risky the odds move in favor of a helmet. This argument only works for safe vehicular cycling below about 15mph)

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    Can you re-word this answer so that there's an actual reason for/against wearing a helmet? – darkcanuck Oct 27 '10 at 23:43
  • @darkcanuck: better? – freiheit Oct 29 '10 at 17:01
  • better, yes. Your argument is essentially that you wouldn't ride if required to wear a helmet, thus impacting your health -- which is perfectly valid. The key sentence I was looking for is "If I felt I had to wear a helmet absolutely every time I got on a bicycle, I'd cycle less and actually reduce my life expectancy." – darkcanuck Oct 29 '10 at 17:10

For Emergency stop where you happen to be on a patch of black ice, you go sideways - ditto a patch of spilled oil on rain-soaked pavement.

Both wipeouts were totally sudden, no chance to land properly. When my shoulder hit pavement, head snapped over, top/side of helmet went "THUNK!".

Just got up & rode away.

Helmets are less ugly than brains spilled onto the street.

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    I think that anecdotes aren't helpful in this thread. – Jay Bazuzi Oct 22 '10 at 4:21
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    I think that the back-it-up principle is the only way topics like this can be justified on a Q-and-A site like SE. – Unsliced Oct 22 '10 at 11:20
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    However you would not have hit your head very hard, so the helmet saved you from a mild knock. Still worth while for the helmet, but not a case of a possible "brains spilled onto the street" – Ian Oct 26 '10 at 11:58

For: Wow... Ride your bike down the road at 20 miles an hour, obeying rules of the road. Have a pickup truck roll through a stop sign an pull directly into your right-of-way path. Hit the pickup, go over the hood and land on the pavement. Note the extremely loud sound inside of your skull: the sound of the helmet absorbing the impact and breaking in 7 places just as it was designed to do, spreading the impact accross 7 different break points instead of one concentrated concussion-inducing, possibly brain-damaging location on your skull. Get up and walk away with only a headache in stunned amazement that people don't want to be inconvenienced by wearing a helmet. Ok, you don't need to wear a helmet 99.99% of the time. But when your head hits the pavement, well, it was totally worth the 25 years of inconvenience. Its up to you, gambler. Odds are pretty good in your favor... But I submit: you'd gladly go back and wear your helmet a thousand times if you could undo the accident you were just in...

  • Ouch! That happens all too often. But - do you wear a helmet in a car? – Jay Bazuzi Oct 27 '10 at 15:12
  • Helmets are designed to crush. A broken helmet has failed. Always wear a skull. – Tom Hawtin - tackline Oct 28 '10 at 0:24
  • @Tom: many helmets are designed to crush and to break apart. If there's no crush they didn't actually do anything to help. – freiheit Jan 2 '11 at 21:39
  • Very dramatic, but how much was the helmet crushed? If there wasn't any, or only very little, the helmet probably didn't do anything to protect you. – freiheit Jan 2 '11 at 21:41

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