How mosquitoes choose

knows what drives the little vampires? Leslie Vosshall of New York’s Rockefeller University believes she might.

There have been theories, over the years, that mosquitoes are more attracted to people with a certain blood type or blood sugar level, to women more than men, particularly pregnant women. But there is little credible data to support these theories, says Vosshall, a neurobiologist at the Howard Hughes Medical Institute at Rockefeller University.

She now has evidence to suggest that the real answer has always been right on the surface. It has to do with carboxylic acids, common organic compounds found on human skin. These make up the oily layer that moisturises and protects skin. And their odour acts like a strobe light to mosquitoes. Odour has long been thought to be a key factor in why some people get bitten so much more, but scientists have been unable to pin down what about an odour was causing the attraction. Now, a study led by Vosshall and published in the journal Cell in October explains how they arrived at carboxylic acid as the answer.

To observe the effects of different body odours on mosquitoes, the researchers asked 64 people to wear nylon stockings on their arms for six hours. Pieces from these stockings were then placed in a box containing dozens of female Aedes aegypti mosquitoes.

The evaluation was conducted in round-robin tournament style. One sample emerged a clear favourite, with an attractiveness score 100 times greater than the least-attractive patch. This was the one with the highest concentration of carboxylic acids. Apparently, the level of affection doesn’t change with time.

With a sample size of just 64, there is still much ground to cover. One looming question, for instance: Why do some people produce more carboxylic acid? While those answers are sought, try not to let this update get under your skin.