We don't fully understand why some people appear more attractive to mosquitoes – largely because it's complicated, a tangled web of physiological factors, geography and species. But a new study has found that for some people, the biting insects are partial to the taste of beer.
Dutch researchers from Radboud University Nijmegen put a theory to the test, conducting an experiment on revelers attending the three-day Lowland music festival in the Netherlands in 2023. The team built an on-site pop-up lab out of shipping containers, which held custom cages filled with thousands of female Anopheles stephensi mosquitoes. Incidentally, this species is a leading vector of malaria in other parts of the world.
The researchers recruited 465 festival-goers to be part of the experiment, which involved a hygiene and event-behavior survey, a breathylizer reading, and a practical test requiring participants to put their left arms against the wall of a transparent cage housing 20–35 female insects. Then a camera tracked how many mosquitoes landed near the skin compared to a sugar feeder on the adjacent side of the cage. Skin swabs were also taken to assess microbiome makeup.
"Participants were asked to present their lower right arm by holding it against the right perforated side of the cage, while placing their arm on an acrylic support to prevent motion and fatigue," noted the researchers. "Perforations in the cage wall allowed skin odorants to diffuse into the cage, while being sufficiently small to prevent mosquitoes from biting through."
What they found was that people who had drank beer in the previous 12 hours at the event were 1.35 times – or 35% – more attractive to the mosquitoes than those who didn't. However, the amber ale wasn't the only lure.
"Mosquitoes showed a clear fondness for those who drank beer over those who abstained from the liquid gold," noted researchers. "Attraction was also contagious: Participants that successfully lured a fellow human into their tent the previous night also proved more enticing to mosquitoes. Meanwhile, skipping the morning showering routine and using sunscreen reduced mosquito attraction. Streptococci were more abundant on the skin of highly attractive individuals, and the overall abundance of malodor associated bacteria was high."
There was no significant attractiveness for wine drinkers found, and no direct link between measured blood alcohol concentration and mosquito landings. In other words, mosquitoes seemed to respond more to the general beer-drinker profile than to the alcohol in the bloodstream. Cannabis use also showed a modest association with increased attraction, but the effect disappeared once other factors were considered.
Hygiene and sunscreen seemed to be a deterrent, with those who had recently showered and applied protection were far less appealing to mosquitoes, with attraction cut nearly in half. The protective effect of sunscreen faded as time since the last shower increased, suggesting that sunscreen may mask natural odors temporarily, or contain compounds that happen to (incidentally) deter mosquitoes. Perfume, by contrast, made no difference, perhaps because the containers were already a heady mix of human and environmental smells.
It might not be the beer itself that attracts mosquitoes but the effect this kind of alcohol has on human skin.
"There have been some experiments in Africa with a particular type of mosquito, where some people had beer, and some people didn't have beer," said mosquito expert Nigel Beebe, an associate professor at the University of Queensland's School of the Environment. "The tests found that the people who’d had beer would be slightly more attractive to mosquitoes. I think when you drink alcohol, you might generate a stronger heat signature (this is caused by the dilation of skin blood vessels), or a stronger olfactory (sense of smell) signature in your CO2 plume (not in the CO2 plume but from the skin), which makes you an easier target for mosquito bites."
When we exhale, we create a CO2 plume – a column or cloud of carbon dioxide drifting away from our body. Mosquitoes have specialized sensors (neurons in their maxillary palps) that can detect tiny rises in CO2 concentrations from several meters away – much farther than they can smell skin odors. It's this, along with thermal signals, that scientists believe lure mosquitoes to a human landing site.
"Different types of mosquitos find their hosts in similar but different ways," said Beebe. "Due to evolution, most mosquitoes are attracted to carbon dioxide (CO2), which is in the air that we exhale. If a mosquito finds what we call a ‘CO2 plume’ and flies up the plume gradient, they’ll inevitably find a host. Once they’ve found you, the mosquito will then detect how much heat you give off, otherwise called your heat signature, as they can prefer warmer hosts.
"Then they will land on your skin and touch you a few times to determine your skin’s oil breakdown products created by your microbiome," he added. "From there, they will find the best place to bite in relation to your skin capillaries, before biting."
It's worth noting that blood type played no role in attractiveness, again supporting evidence that debunks the long-held belief that this is a factor in who mosquitoes choose to target.
Yes, the study has plenty of limitations – participant selection, lingering odors within the high-traffic shipping containers and other factors not assessed in the research survey. And while it's a rather unconventional study setting, it does, however, offer hints as to how people can protect themselves best while sharing the environment with mosquitoes – some of which can spread diseases such as malaria and dengue fever.
"The general picture that emerges from our study suggests that a sober lifestyle – abstaining from drugs and alcohol, sleeping alone and applying sunscreen regularly – lowers one’s chances of getting bitten by mosquitoes," the team noted. "While we found no evidence supporting popular myths such as blood type influencing bite frequency, we were unable to assess the existence of so-called ’sweet blood.’ Ultimately, enjoy the next festival or camping trip as you like – but it seems mosquitoes may have a soft spot for those making less responsible choices."
On the upside, if you forget your insect repellent when outdoors, you could better your chances of avoiding bites by at least making sure you have plenty of sunscreen.
Source: Radboud University Nijmegen via Phys.org
