Wearing a helmet could actually make people less safe because they are more inclined to take greater risks, new research has claimed.
The University of Bath study measured sensation-seeking behaviour and analysed risk taking in adults aged 17-56 using a computer-based simulation.
Splitting participants in two groups - one wearing bicycle helmets and the other baseball caps - they had to blow up an on-screen balloon.
Test subjects were given more points per inflation, but would lose all their "earnings" if the balloon popped.
The results showed the group wearing helmets were more inclined to take risks and inflate the balloon the most.
Dr Ian Walker and Dr Tim Gamble said their study called into question the effectiveness of certain safety advice - including using helmets for various leisure activities such as cycling.
The pair also believe it could have wider implications for soldiers on the battlefield.
Dr Walker said: "This could mean that people using protective equipment might take risks against which that protective equipment cannot reasonably be expected to help.
"Several studies in the past have looked at so-called 'risk compensation', suggesting that people might drive differently when wearing seatbelts, or make more aggressive American football tackles when wearing helmets.
"But in all those cases, the safety device and the activity were directly linked - there's a certain logic to sports people being more aggressive when wearing equipment that is specifically intended to make their sport safer.
"This is the first suggestion that a safety device might make people take risks in a totally different domain."
Dr Gamble said: "This is not to say that people shouldn't wear safety equipment, but rather to say that the whole topic is far more complicated than most people think.
"We need to be mindful of the unintended consequences which might exist and not just apply 'common sense' when it comes to addressing safety concerns.
"If feeling protected does make people generally more reckless - which is what these findings imply - then this could affect all sorts of situations, perhaps even how soldiers make strategic decisions when wearing body armour."