THAT'S THE WHY:  We are not overly hairy creatures – at least compared with non-human primates – but we still have fine hairs on our bodies. Why?

Perhaps one reason is to help warn us against impending parasite attack. That’s the scenario tested by a new study which shaved patches of fine body hair off volunteers to see what would happen when a parasite came calling.

“Despite our hairless appearance, the human body has the same density of hair follicles as would be expected of an ape of the same size,” write the researchers in Biology Letters.

Could it be that we retained fine hair because it’s useful for warning that external parasites are on the prowl?

For the experiments, the researchers at the University of Sheffield recruited 29 participants through Facebook.

Each volunteer had a section of hair shaved from the upper side of one forearm, while the other arm was left unshaven as a control.

Volunteers looked away as bedbugs (Cimex lectularius) were introduced to the patches and each participant used a tally counter to register when they felt something on their arm.

The presence of fine hair appeared to prolong the search behaviour of the insects and enhance the detection of the parasites – and hosts with a higher hair index were more likely to detect them.

“Our findings show that more body hairs mean better detection of parasites,” says researcher Prof Michael Siva-Jothy .

“The hairs have nerves attached to them and provide us with the ability to detect displacement.

“By forming a barrier and providing detection, these hairs prolong search time and make detection more likely because the bug has to spend more time clambering over them.”