Do bicycle helmets also have adverse effects?

Answer

Only a few studies find indications that cyclists wearing helmets will behave less safely, or that other road users will do so in their presence (behavioural adaptation), but most studies do not find any evidence of these unintended adverse effects. The occasionally voiced assumption that bicycle helmets lead to more neck injuries lacks sufficient proof. The effect of (mandatory) helmets on the use of bicycles is not unequivocal. Below, each of these possibly adverse effects is explained.

Behavioural adaptation

Some researchers claim that the positive effects of bicycle helmets are limited because cyclists adapt their behaviour (e.g. behavioural adaptation or risk compensation, amongst others in [40]. Helmeted cyclists would supposedly feel safer and would show riskier cycling behaviour. The opposite effect of associating helmet use with safer cycling behaviour is also found. It is unclear whether cyclists behave more safely because of their helmets or, more probably, whether cyclists inclined to cycle safely anyway, use helmets more often. Systematic literature reviews [41] [42] show that empirical evidence for behavioural adaptation due to mandatory helmet use is not unequivocal.

Other road users may also adapt their behaviour: they may behave differently towards helmeted cyclists than towards unhelmeted cyclists. A British study [43] explicitly examined this. It showed that drivers of motor vehicles kept less distance to cyclists with helmets than to unhelmeted cyclists. A possible explanation is that motorists consider helmeted cyclists to be more skilled than cyclists without helmets, and therefore use smaller safety margins. However, re-analysis showed that the distance was unchanged, which therefore led to different conclusions. Further research is needed to determine how robust this (at this stage) one-off finding is (see [44] [45] for a discussion).

Neck injury

It is assumed that the extra weight of the helmet and possible friction with the road surface [46] increase the risk of neck injuries [47]. Yet, in recent meta-analyses of the effect of bicycle helmets [28] [29] no increased risk of neck injury was found.

Bicycle use

A frequently voiced argument against the mandatory use of bicycle helmets is that this would have an adverse effect [48] on bicycle use. Several international studies do indeed show a decrease in bicycle use, even though most studies do not find such an effect or only find a temporary effect [9] [42]. Also see the question What is the effect of helmet use on the popularity of cycling?.

Part of fact sheet

Bicycle helmets

A bicycle helmet is intended to protect cyclists against head and brain injuries when they are involved in crashes.

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