“There’s even a case to be made that helmets actually increase the risk of injury. Institute of Transport Economics researchers Aslak Fyhri and Ross O. Phillips ‘found that after having removed their helmets, routine helmet users cycled more slowly and demonstrated increased psychophysiological load.’ In other words, helmet-wearers might be engaging in riskier cycling behavior than they might if they went bare.”
Read the entire article at Grist.org: Do helmets really keep cyclists safer?