Sorry I am new in bicycling , but I think the head is least like to be in contact with any other things during crash normally down from head rather the head might come in contact in other vectors . So I am curious how effective bicycle helmates are .
I think the head is least like to be in contact
It's true that there are many times I've fallen off without hitting my head ... especially at low speed.
I often put my hand on the ground -- and that's one reason why I like to wear padded/leather cycling gloves.
On the other hand if you do hit your head then a helmet can be helpful. One time I fell off (skidding on a corner with my feet clipped to the pedals) and I hit the ground before I knew it, and hit my head. Not wearing a helmet, that meant a trip to the hospital and several stitches (and a warning that I ought to use a helmet).
If you do hit your head without a helmet then a scalp wound with stitches might be the best that can happen (the worst might be concussion, brain injury, skull damage).
Bicycle helmet is to protect the head, which has the most important organ in human. You could still live a normal life even with broken/ lost limb(s). But a head injury could change your life forever. A helmet is like a wall between life and death. The priority goes by protecting the most important thing to you first (i.e. your life), not by preventing the most common injury.
Having a priority list, you could fulfil the ' safety pyramid' for extra protection, e.g. helmet, arm/leg guard, gloves, boots. However, it is impractical to get a full body armour for just cycling. The risk of body injury that could lead to life and death situation whilst cycling is rather small. Thus, this is often ignored.
As Frisbee also mention, the brain is also a very sensitive organ. Yet, a seemingly 'minor' damage to the brain is often lethal. Therefore, the head needs protection, albeit a small possibility.
I have witnessed two head injury accidents (while cycling) in my life. One happened a few building block away from my house. It was a classic cornering accident type. The person lost balance (clipped the pavement), and hit her head directly to the pavement (no helmet). She unfortunately pronounced dead at the scene.
The second incident happened on the street. The person was riding in a freezing condition. It is with such unfortune that the person lost control on a straight road and hit his head on the raised curb. He is fiancé of my wife's friend. He is still in coma at this moment (since 3 years ago).
Needless to say, your argument is flawed. It is similar to a statement that: 'I have never been in an accident that an airbag is activated, so is airbag redundant?'
There is no definite yes or no answer whether helmets are effective. It is a choice which level of risk you want to accept, balanced against the inconvenience. When you search for "bike helmets", you'll quickly see that the arguments are very heated without much agreement.
It is true that traumatic brain injuries are terrible, and if you hit your head, it's often (not always) better to have a helmet. However, to evaluate the risk you also have to take into account how likely it is to hit your head. Traumatic brain injuries also happen with similar likelihood when walking (stumble, slip on ice and hit your head on the kerb), in buildings (slippery floor after wiping...), or when being hit by a car that mounts the pavement or indeed being hit by a bicycle. Most people don't even think about those risks and don't wear a helmet all the time when walking or driving or when wiping the kitchen floor, so it is somewhat inconsistent that bicycle helmets are so intensely promoted.
The actual risk depends very much on your riding style and environment. If you ride really fast, or do mountain biking, or perhaps you are a bit unstable or have a medical condition that you may lose balance, then the risk is higher and it makes sense to chose a helmet.
However, if you are a slow cyclist, have good cycle paths and are generally a careful cyclist, then the risk isn't any higher than the risk of falling when you walk, so in this group many chose quite logically not to wear a helmet.
Other people may wear a helmet in winter when they know there can be icy patches on their commute, but not in summer when the risk of falling is much less.
So it's really a personal choice if you think your personal risk, depending on riding style, ability and environment, is higher than the risk of falling or getting into a collision when you walk.
Additional note: Be cautious about drawing conclusions from personal anecdotes. You'll find lots of stories of the type "wearing a helmet saved my life" and "didn't wear one and suffered terrible injuries". It is usually not possible to know if an injury could have been avoided with a helmet. Helmets absorb only very limited amounts of energy, so if you e.g get hit by a truck's wing mirror the helmet will do virtually nothing as the energy is just too high.
The word effective is being used in different ways
Is a helmet mechanically effective protecting the head. Yes it is. There are testing standards. I can put on a helmet and hit it with a stick and not even feel it where that same force on skull would draw blood.
UCI requires helmets. The NFL and NHL require helmets. In my city under 18 you must wear a helmet.
Then there is statistically effective. Is there statistical proof that the use of helmets actually reduced head injuries. Based on the amount of data it is likely to be inconclusive. No one is going to commission a controlled study of people to ride with and without helmets. They know darn well a helmet protects and they are not going to put people at risk - that is lawsuit waiting to happen. Even with review of hospital records if you have an equal portion of traumatic head injuries you cannot conclude helmets were not effective. There is good chance the people with helmets were going faster.
I don't need statistics or a slide rule to know a helmet is going protect my head.
If you need statistics to decide if a helmet is effective then be prepared to become a statistic.
Risk / convenience management
With anything you take risk. Driving to store in your car you take a risk. You mitigate risk by wearing a seat belt. In the early days a lot of people did not wear seat belts (and even some don't today). One of the excuses was - not yet proven they actually save lives.
There is actual risk and perceived risk and some people are risk averse and some are risk tolerant.
The OP asserts most vector don't include the head so is it effective? The problem with that logic is a force to the head becomes serious or even life threatening with a relatively small amount of force. If you land on a rock hard enough to break an arm that same force on an unprotected skull is easily life threatening.
There also is this vector of hit by a car.
As your speed goes up so does your chance of fall and severity impact. At very low speed and nothing out of your control (like a car) then the risk is manageable. The risk of a severe brain injury is very very low even without a helmet. A helmet still does provide protection.
In the winter when it is raining or snowing I wear a rock climbing helmet with a climbing jacket that will go over the top. A friend of mine said but it is not as safe as a certified bike helmet and my response was the helmet I am wearing is a lot safer than the helmet I am not wearing.
The NBA does not require helmets. It would alter play and there is not enough speed for a likely severe skull energy. And they are pros that control their falls.
If I am going to ride less than 10MPH and no cars then no helmet is a fair risk / convenience management. Yes in Holland with segregated cars going to market at low speed is fair risk / convenience management. The OP is new rider Nepal.
A buddy of mine bother's died playing basketball. They set up one of those mini tramps and were doing dunks. He hung on the rim swung forward lost his grip and landed on his head and boom dead.
I know a guy that hopped his front wheel doing less than 10 mph and lost the front wheel. He went out the front without a helmet and spent 6 weeks in the hospital. He wears a helmet now.
I was practicing low speed bunny hops and went out the back with a helmet on. I still passed out for while and had a terrible headache. That would have been a trip to the hospital and potentially life threatening without a helmet.
Look for reasons to wear a helmet not for excuses not to wear a helmet.
Buy a good helmet. A $100+ helmet rides a lot nicer and has better ventilation. Ride with your helmet firmly strapped.
I would recommend using a bicycle helmet, at least if you are a beginner, drive in traffic, with lots of other actors (pedestrians, other riders and unexpected stuff) and don't have full control of the environment around. I once had an accident, I fell on my hands first and afterwards my head hit the road with the helmet on. Afterwards I had twisted wrists and broozes in my head. I always imagine what was the case without my helmet. witnessed couple of accidents before, where the rider encounters an unexpected obstacle in front so basically even if you try to brake you will fall in front of the bicycle with head first. this is what happened and in one of the cases they cycler was safe although the helmet was totally damaged.
Not to scare you, if you ride around the building or in an empty roads probably 99.9% of times it is safe. Just in the rides you feel you might not have full control please take all protections needed.