If 2 tons of steel hit you at 40mph+, you will die. You can be dead wearing a helmet if you wish.

Trying to find a way out of that situation is futile, you're trying to fight the laws of physics. The solution is to not be there in the first place, not trying to add 5cm of padding on top of your head.

The way to do so, at policy level, is building a network of dedicated cycling paths physically separated from motor traffic and protected intersections where bike traffic is priviledged over motor vehicles.

But regardless of the state of infrastructure, recommending helmets to cyclists has overwhelmingly negative consequences. The minor safety benefits pale in comparison to the damage done by the reduced amount of bicycle trips caused by the friction introduced by needing a helmet. Cycling has such immense benefits that virtually any reduction in trips due to helmet advocacy will have devastating health outcomes. This isn't a matter of comparable numbers that can be discussed either, we're talking orders of magnitude here.

If the above is unconvincing, some research follows (quotes presented to be read in order):

[1]: "Cycling UK wants to keep helmets an optional choice. Forcing - or strongly encouraging - people to wear helmets deters people from cycling and undermines the public health benefits of cycling. This campaign seeks to educate policy makers and block misguided attempts at legislation."

[2]: "Even if helmets are 85% effective (and assuming q = 0.5 as above), the number of cyclists’ lives saved will still be outnumbered by deaths to non-cyclists if there is a reduction in cycle use of more than 2%"

[3]: "Enforced helmet laws and helmet promotion have consistently caused substantial reductions in cycle use (30-40% in Perth, Western Australia). Although they have also increased the proportion of the remaining cyclists who wear helmets, the safety of these cyclists has not improved relative to other road user groups (for example, in New Zealand).

The resulting loss of cycling’s health benefits alone (that is, before taking account of its environmental, economic and societal benefits) is very much greater than any possible injury prevention benefit."

[...]

"Evidence also suggests that even the voluntary promotion of helmet wearing may reduce cycle use."

[...]

"Even with very optimistic assumptions as to the efficacy of helmets, relatively minor reductions in cycling on account of a helmet law are sufficient to cancel out, in population average terms, all head injury health benefits."

[4]: "With 290 cyclist fatalities in 2022, cyclists were the largest group of road casualties. Of these, most were killed by collision with a vehicle (206 bicycle deaths)."

[5]: "Cycling levels in the Netherlands have substantial population-level health benefits: about 6500 deaths are prevented annually, and Dutch people have half-a-year-longer life expectancy. These large population-level health benefits translate into economic benefits of €19 billion per year, which represents more than 3% of the Dutch gross domestic product between 2010 and 2013.3.

The 6500 deaths that are prevented annually as a result of cycling becomes even more impressive when compared with the population health effects of other preventive measures. In an overview, Mackenbach et al.11 showed that the 22 new preventive interventions that have been introduced in the Netherlands between 1970 and 2010 (e.g., tobacco control, population-based screening for cancer, and road safety measures) altogether prevent about 16 000 deaths per year.

Still, our results are likely to be an underestimation of the true total health and economic benefits."

[6]: "Riding a bicycle to work every day reduces the risk of premature death by 41% (risk of dying from heart disease: -52%; risk of dying from cancer: -40%)."

[...]

"Regular cycling boosts physical fitness and compares to 1 to 2 weekly gym sessions."

[...]

"Bicycle use not only improves physical health, but also has a positive impact on mental health and subjective well-being."

[1]: https://www.cyclinguk.org/campaign/cycle-helmets-evidence

[2]: https://www.cyclehelmets.org/1249.html

[3]: https://www.cyclinguk.org/article/why-should-highway-codes-a...

[4]: https://english.kimnet.nl/publications/publications/2023/11/...

[5]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4504332/

[6]: https://www.government.nl/binaries/government/documenten/rep...