Are bicycle helmets dangerous?


Bicycle helmets can mitigate minor skull injuries like bruises and lacerations at low speeds.


Contrary to popular belief, helmets do not protect against brain injury.

On the other hand, helmets tend to:

  1. increase the risk of accidents
  2. increase the risk of the head hitting the road
  3. increase the risk of neck injury
  4. increase the risk of brain injury

It is not safe to assume that the protection provided by a helmet outweigh these risks.


Some politicians have claimed that “Helmets save lives“.

Is this true?  CRAG has asked for evidence, but the Australian government has been unable to provide any.

Even helmet salespeople do not make such claims. After being asked

Can your helmet save your life?“,

a helmet manufacturer salesperson shrugged and laughed uncomfortably, before responding

Can it?” “Well, not save your life, no.

What is it that politicians know that helmet salespeople don’t?

What protection do helmets provide?

soft-shell-helmetA bicyle helmet is a piece of polystyrene covered by a layer of plastic less than 1mm thick.
It can protect in a minor accident.  However, it is not designed to protect in a serious accident.

Bicycle helmets are a piece of styrofoam designed to protect in minor impacts:

“In cases of high impact, such as most crashes that involve a motor vehicle, the initial forces absorbed by a cycle helmet before breaking are only a small part of the total force and the protection provided by a helmet is likely to be minimal in this context. In cases where serious injury is likely, the impact energy potentials are commonly of a level that would overwhelm even Grand Prix motor racing helmets. Cycle helmets provide best protection in situations involving simple, low-speed falls with no other party involved. They are unlikely to offer adequate protection in life-threatening situations.“

In serious accidents, they tend to disintegrate on impact, absorbing little energy. This crumbling is what many people ironically mistake the helmet for as having saved their life:

“The next time you see a broken helmet, suspend belief and do the most basic check – disregard the breakages and look to see if what’s left of the styrofoam has compressed. If it hasn’t, you can be reasonably sure that it hasn’t saved anyone’s life.“

Dr Carwyn Hooper from St George’s University in London reports:

“Looking at evidence, it does not matter if people are wearing a helmet or not, any serious accident on a bike is likely to kill them,”

Bicycle helmets are useful in protecting against bruises and minor lacerations. Yet, despite the protection they provide, the adoption of helmets has not been followed by a reduction in injuries. Surprisingly, the bicycle helmet law in Australia has resulted in a large INCREASE in cycling injuries:

After a helmet law was introduced in Australia, the rate of cycling injuries tripled.

How can the widespread wearing of helmets increase the risk of injuries?

There is more to bicycle helmets than the protection they provide. Helmets can affect the behavior of cyclists in unexpected ways, leading to an increase in accidents and injuries.

Although helmets protect, they can also increase the risk of accidents.

Increase risk of accidents

A false sense of safety can induce people to take more risks, leading to more accidents and more injuries. This tendency is called risk compensation, a well-known safety factor as reported here:

“the law of unintended consequences is extraordinarily applicable when talking about safety innovations. Sometimes things intended to make us safer may not make any improvement at all to our overall safety”

risk-compensationRisk compensation is the tendency to take more risks when wearing safety equipment.
Lured by a false sense of safety, helmeted cyclists tend to have more accidents.blank

Wearing a helmet can induce cyclists to take more risk, sometimes with serious consequences, as reported in the New York Times:

“the increased use of bike helmets may have had an unintended consequence: riders may feel an inflated sense of security and take more risks. …

The helmet he was wearing did not protect his neck; he was paralyzed from the neck down. …

”It didn’t cross my mind that this could happen,” said Philip, now 17.
”I definitely felt safe. I wouldn’t do something like that without a helmet.” ”

1989 study found that helmet wearers were 7 times more likely to have accidents. How can a flimsy piece of polystyrene compensate for 7 times more accidents?

Helmets accidents cycle

Risk compensation affects not only cyclists but also motorists who tend to be less careful around helmeted cyclists. As reported in a study published by the University of Bath in the UK:

“Bicyclists who wear protective helmets are more likely to be struck by passing vehicles”

Both the behaviour of the helmeted cyclist and surrounding motorists tends to increase the risk of accidents.

Children are particularly affected by risk compensation, as reported in Accident Analysis and Prevention :

“Results indicated that children went more quickly and behaved more recklessly when wearing safety gear than when not wearing gear, providing evidence of risk compensation. Moreover, those high in sensation seeking showed greater risk compensation compared with other children.”

Another factor in risk compensation is that helmets tend to encourage people to ride faster, as reported in 2011 by the Risk Analysis international journal:

“those who use helmets routinely perceive reduced risk when wearing a helmet, and compensate by cycling faster

Riding faster tends to increase the severity of injuries in case of an accident.

Many people believe that bicycle helmets protect against brain injury. Unfortunately they can’t. They are not designed to protect against the major cause of brain injury.

What causes brain injury?

The design of current bicycle helmets is based on an obsolete theory that believed that brain injury was due to linear acceleration, from the head hitting a wall for example.  More recent research has shown that the main cause of severe brain injury is rotational injury, from the head turning quickly.  The skull may not be damaged, but there can severe internal brain injury.  This article reports from a surgeon who operates on cyclists:

” “The ones with brain swelling, that’s diffuse axonal injury, and that’s bad news” …

the whole brain is shaken up, creating many little tears in its inner structure …

Such patients undergo personality change, can contract epilepsy and have difficulty controlling their anger. They might become unemployable. Depression is a common accompaniment to brain injury. Rosenfeld sees patients’ families shattered, too. “They’re never the same. It often leads to marriage disharmony and family breakdown.” …

Rosenfeld’s opinion is candid. “I don’t know if [helmets] do much to protect the inner part of the brain,” “

Helmets cannot protect against rotational injury but they can increase it, according to research done in Sweden:

“The non-shell helmet did in all trials grab the asphalt surface, which rotated the head together with
the helmet. The consequences were in addition to the rotating of the head, a heavily bent and compressed neck, transmitted on through the whole test dummy body after the impact.  …

This gives an average angular acceleration of 20800 rad/s² for rotating the head from 0 to 0.26 rad during the 5 ms. Löwenhielm proposes 4500 rad/s² to be the maximum angular acceleration that can be tolerated for a limited time period, which also is suggested by Gilchrist and Mills.”

Soft-shell helmets grabbed the road surface, and then amplified rotational acceleration to four times higher than the tolerable maximum.

On impact, the larger head volume amplifies rotational acceleration.  A study done in the UK reports that a difference of just 3cm in helmet circumference increases rotational acceleration by 150%:

“the 3000rad/s² to 8500rad/s² measured during abrasive and projection oblique tests with size 54cm (E) helmeted headforms. However, for the most severe cases using a size 57cm (J) headform, rotational acceleration was typically greater than 10,000rad/s² and increased to levels of 20,000rad/s², a level at which a 35% – 50% risk of serious AIS3+ injuries is anticipated.”

The difference between a helmeted and non-helmeted head is about 20cm.

The tendency for helmets to amplify rotational acceleration is a serious flaw in their design. Rotational brain injury can be a permanent, debilitative injury. It is essential to mitigate those risks.

Increase risk of the head hitting the road

In the event of an accident, helmets increase the risk of the head hitting the road.  Helmets increase the volume/size of contact area of the head. This study reports that helmeted riders are more than twice as likely to hit their head in an accident, with the additional impacts being to the sides. This is consistent with post-crash studies that found that most helmets show impacts to the side, areas where a bare head may not have been hit.


Helmets increase volume of the head, doubling chance of the head hitting the road in an accident;
The larger volume also amplifies rotational acceleration, the main cause of brain injury.

Those  additional side impacts when helmets are worn are particularly dangerous, as they tend to generate high rotational acceleration, that is amplified by the higher volume of the head + helmet.  This amplified rotational acceleration can cause severe brain injury that may not have happened without a helmet.

A 1988 study found that helmeted riders report hitting their heads seven times more often than un-helmeted riders.  A bare head, often protected by the shoulders, provides the lowest risk of head contact in the event of an accident.

Helmets are not suitable for children’s more deformable head

The standard bicycle helmet is not adequate for children more flexible heads.  In 1987, the Federal Office of Road Safety, a government agency, completed research on helmets that highlighted several serious deficiencies with bicycle helmets:

The substantial elastic deformation of the child head that can occur during impact can result in quite extensive diffuse brain damage. It is quite apparent that the liner material in children’s bicycle helmets is far too stiff …

rotational accelerations were found to be 30% higher than those found in similar tests using a full face polymer motorcycle helmet. More work needs to be done in this area as there would seem to be a deficiency in rotational acceleration attenuation that may be the result of insufficient shell stiffness. 

child cycling 4

Bicycle helmets helmets are designed for adult heads. They are too stiff for children more deformable heads.  Despite this, helmets are promoted as “protecting” children, without appropriate warnings.

Helmets are associated with more severe brain injuries

doctor from New Zealand reports that helmets convert what would have been focal head injuries into much more debilitating brain injuries:

“cycle helmets were turning what would have been focal head injuries, perhaps with an associated skullfracture, into much more debilitating global head injuries”

Cycling injuries data from Canada  reports that the length of stay in hospital increased following helmet laws, from 4.3 days to 6.9 days, suggesting more severe head injuries.  In addition, the number of serious head injury admissions increased by 46% from 2000-2001 to 2003-2004.

Do helmets provide a net safety benefit?

A helmet protects by absorbing the energy of the impact through compressing the polystyrene layer. If the polystyrene has not compressed, but has broken into pieces instead, it indicates that the helmet has failed. It may have prevented bruises & lacerations, but it didn’t do much to reduce the energy of the impact. Yet ironically many people mistakenly believe that a broken helmet “proves”  that a helmet has saved them.

Bicycle helmets are a safety trade-off. They can reduce focal skull injuries from linear acceleration in minor accidents. However, they increase the chance of the head hitting on impact, particularly side impacts that generate high rotational acceleration, potentially aggravating brain injury.

Bicycle helmets provide limited protection while increasing the risk of neck injury and brain injury. It is doubtful whether soft-shell helmets do much to prevent focal brain injuries, as there is no hard shell to take the blow.

It is doubtful whether soft-shell helmets provide a net safety benefit.  Evidence provided in court is telling:

“So in at least one case now, a High Court has decided that the balance of probability was, in the matter before the Court, that a cycle helmet would not have prevented the injuries sustained when the accident involved simply falling from a cycle onto a flat surface, with barely any forward momentum. …

the QC … repeatedly tried to persuade the neurosurgeons … to state that one must be more safe wearing a helmet than would be the case if one were not. All three refused to do so, claiming that they had seen severe brain damage and fatal injury both with and without cycle helmets

recent meta-analysis of helmets effectiveness reports that there seems to be no net beneficial effect overall from soft-shell helmets. They protect against skull injuries in low-speed accidents, but do not protect against facial injuries, and increase the risk of neck injuries.

It is not safe to assume that the padding provided by helmets outweighs the increased risk of accidents, and the risk of aggravating neck and brain injuries.

The belief that helmets can only improve safety may be a myth:

“Bicycle helmets might not protect cyclists much at all.  And, in fact, in some cases, they might actually be more dangerous than going lidless. …

head injuries had increased even though the use of helmets had skyrocketed throughout the 1990s.  The risk of injury per cyclist had gone up by 51%. …

We don’t know what’s going on,” said one political appointee who should know.  Well, I’ll offer my idea.  People accepted the idea that helmets work, and then created studies to “prove” that they do. “

While a helmet might protect IF you have an accident AND it is at low speed AND you fall on your head, is it really worth the increased risk of having an accident?

We do not know whether helmets provide a net safety benefit. What we do know is that cycling has become more dangerous after the helmet law, by increasing the risk of death & serious injury by 50% for child cyclists in NSW. 

The UK’s National Children’s Bureau provided a detailed review of cycling and helmets in 2005, concluding that the case for helmets is far from sound:

“The conclusion from the arguments outlined above is that the case for cycle helmets is far from, sound. The strong claims of injury reduction made by helmet proponents have not been borne out for fatalities (which this paper argues is the most methodologically sound test of effectiveness) in real-life settings with large populations. …

the benefits of helmets need further investigation before even a policy supporting promotion can be unequivocally supported. ….

The cycle helmet debate shows the dramatic power of real life events in shaping our understanding of causality. Tragedies happen; child cyclists are killed or left disabled for life; and we cannot let go of the belief that something 
could and should have been done to stop that particular event from happening – especially when that something is so simple as wearing a helmet. We find it hard to accept that the helmet may have made no difference. We find it harder to accept that encouraging or forcing children to wear helmets might also encourage them to ride in a more dangerous way and paradoxically to increase the risk that they will suffer an accident. And we find it much harder to accept that compulsory helmet use might put children off cycling altogether, leaving them less physically active, and – many years later – more likely to die of heart disease.Think of all the uncertainty behind that line of argument, compared with the seeming rock-solid conviction that a helmet could have saved that particular child’s life, at that particular time. And of course the fact that we are talking about children, who have a claim on our protection and who are still getting to grips with the world, makes it so much more difficult to accept the limitations on our ability to prevent them coming to harm. We cannot ignore the human suffering, pain and loss that lie behind the research and statistics. But our response to it demands reflection and perspective as well as sympathy and conviction.

Is it worth to increase the risk of severe brain injury for the benefit of mitigating minor skull injuries? This dilemma about the trade-off between protection in minor accidents vs. risk of brain injury is what enabled an Australian cyclist to successfully challenge a helmet fine on the basis that wearing a helmet could be dangerous.   After reviewing evidence in a court of law, NSW District Court Judge Roy Ellis concluded:

“”Having read all the material, I think I would fall down on your side of the ledger …

I frankly don’t think there is anything advantageous and there may well be a disadvantage in situations to have a helmet  and it seems to me that it’s one of those areas where it ought to be a matter of choice.

When reasonable doubt exists about any product providing a net benefit, people should have the right to choose.

But what about the studies that claim that helmets protect against 80% of head injuries?

There have been many “studies” claiming that helmets protect against brain injuries. The most famous of those was conducted by helmet lobbyists and financed by the helmet industry. With such conflicts of interests, it is not surprising that the “study” was riddled with methodological errors resulting in exaggerated estimates of helmets effectiveness. Despite this, this research was widely embraced within the medical community, who was eager for an apparent solution to the dreadful incidences of chronic disability from brain injury.

This research became a model for further “research” replicating its flaws and bias. Such research, based on small samples, tends to jump to a premeditated conclusion far too eagerly, with a disturbing lack of scientific discipline. Many “studies” start from the assumption that helmets save lives and attempt to “prove” it by selectively looking for data that supports the predetermined conclusion. Such a biased approach leads to flawed and misleading studies. Many studies exaggerate the protection provided by helmets while ignoring the increase in accidents.

The US government has dropped the claim that bicycle helmets reduce 85% of head injuries, after they were unable to back it up with evidence.

Governments who enacted helmet law have funded “studies” defending their policy.  Such policy-driven studies have been used to cover up the failure of the helmet law.  Official evaluations of the law commonly employ biased selection of research and statistics, resulting in benefits being unduly attributed to the helmet law and adverse effects (like a decline in cycling or an increase in the risk of accidents) ignored. Bill Curnow, once a scientist from the CSIRO, wrote as a conclusion in a scientific article:

“Compulsion to wear a bicycle helmet is detrimental to public health in Australia but, to maintain the status quo, authorities have obfuscated evidence that shows this.”

After several failed attempts to justify its policy through misleading “studies”, and following CRAG submission to the Prime Minister in 2009, the federal government abandoned its compulsory helmets policy.

Many of the studies exaggerating the benefits of helmets make physically impossible claims.

How can helmets reduce 80% of head injuries considering they don’t cover the face where 70% of head injuries are?


Injuries to the skull (the part of the body a helmet covers) constitute 10% of cycling injuries,
or 30% of what is usually classified as head injuries (including face injuries).

How can helmets reduce 88% of brain injuries considering they cannot protect against the main cause of brain injury, rotational acceleration, and they can increase rotational acceleration?

How can these studies make such physically impossible claims? Like this study, many of these studies fail to consider confounding factors, a common error in statistics. They reach unwarranted conclusions far too eagerly. Other examples of misleading research can be found here.

Some deceptive “studies” compare helmeted cyclists in bicycle paths with unhelmeted cyclists on roads. They attribute all the difference to helmets, ignoring the more dangerous road environment. This is an example of failing to consider confounding factors, a common mistake among helmet studies.

Some government studies not only contain false claims, but fail to rectify them after being corrected.

In 2000, the Australian Transport Safety Bureau (ATSB), a federal government agency, released a meta-analysis, that claimed to provide

overwhelming evidence in support of helmets for preventing head injury and fatal injury“.

This claim was rebutted in 2003, the study highlighting that:

“the meta-analysis … takes no account of scientific knowledge of [brain injury] mechanisms”

The government agency did not reply to the rebuttal, effectively giving up on its claim.  Despite being discredited, this analysis is still used by government to defend its policy.  This study was re-assessed in 2011 by an independent researcher who concluded:

This paper … was influenced by publication bias and time-trend bias that was not controlled for. As a result, the analysis reported inflated estimates of the effects of bicycle helmets …

According to the new studies, no overall effect of bicycle helmets could be found when injuries to head, face or neck are considered as a whole

Publication bias is the tendency to cherry-pick studies that suits a particular predetermined conclusion.

How can such misleading “studies” be justified as a form of public service?

Such deceptive studies add little to scientific knowledge. They exaggerate the reduction of minor injuries while ignoring the increased risk of serious injuries. This tends to mislead policy makers towards false “solutions” to cycling safety, while neglecting more effective measures that tend to focus on reducing the risk of accidents.

This might explain why Australia has one of the worst cycling safety record among developed countries, with a fatality rate 5 times greater and a serious injury rate 22 TIMES greater than best practice. For urban cycling, the fatality rate per commuter cyclist is 27 times higher in Sydney, Australia than in Copenhagen, Denmark.

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4 Responses to “Are bicycle helmets dangerous?”

  1. Alan Dow says:

    In 1965, none of us wore helmets. How on earth did we survive?

    I think I landed on my head three times coming off bikes as a child aged about 10-12 years, with resultant bruises and perhaps some minor lacerations. One of the prangs actually caused me to lose consciousness for 10 minutes or so.

    Now of course the helmet fanatics would say all of that could have been prevented if I’d had a helmet on, but that would be a load of twaddle.

    Perhaps I should clarify. In two of the accidents, including the one which caused loss of consciousness, the point of contact was on my face – in areas not covered by helmets at all – the forehead, and the cheekbone.

    In the third accident, I somersaulted over the handlebars, landing with arms outstretched, so that there was no direct impact to my head. There was however, a sliding contact between my head and the ground – exactly the situation where wearing a helmet can exacerbate rotational and whiplash injuries. As it was, I walked away from that one with some minor lacerations which were healed within a few days. Of course, I count myself lucky to be alive, because if I’d been wearing a helmet I ‘would have been killed, for sure’.

    I note one other issue which has not been mentioned above – and that is the possible risk attached to putting polystyrene coffee-warmer insulation around your head while pursuing vigorous exercise. ( Refer ‘Radiator theory of human evolution’ for the crucial role of cranial blood flow in cooling the brain. Yes – it’s a theory – but if the theory is correct, is it really worth the risk of putting insulation around nature’s thermal regulation mechanism for the brain ? )

  2. some guy called guy says:

    You seriously suggesting to people that they shouldn’t wear helmets?

    I’d be embarrassed to peddle such circumstantial “evidence” about something so serious.

    You seriously saying you would rather your head hit the ground with no helmet on?

    • admin says:

      Circumstantial evidence? Did you bother look at some of the evidence provided above?
      “safety in numbers” and “risk compensation” are not circumstantial evidence. They are well known safety phenomena.
      The doubling of the risk of accidents after a helmet law was imposed in Australia is not circumstantial evidence.
      The significant increase in the risk of death & serious injuries after a helmet law was imposed in Australia is not circumstantial evidence.

      What is ironic is that it is helmet believers who rely on anecdotes.

      The helmet ideology is perverse. Helmet zealots believe that accidents are unavoidable, almost normal. They fail to consider that, without a helmet, cyclists may ride a bit more cautiously and not have so many accidents. Many end up in hospital, with broken arms, broken kegs and other injuries.
      Statistically, one can expect a severe head injury from cycling once every 8,000 years of average cycling. Yet for helmet believers, every fall without a serious head injury is “proof” that their helmet saved them from a dreadful brain injury.
      On the other hand, cyclists who don’t wear helmets tend to ride slower and have fewer accidents. Most of them have neither accident nor head injuries, yet they don’t preach that their lack of helmet saved them.

      You are correct. It is serious. The helmet ideology has done serious damage to cycling, by both reducing the number of cyclists and increasing the risk of injuries.

  3. David Blackmore says:

    Why are these things called a “helmet”?
    They don’t seem very different from the polystyrene wrapping protecting a new washing machine.

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