Why are some people more attractive to mosquitos?
Also in this week's column:
- Does eating fish improve brain function?
- What is a Cro-Magnon man?
- How can objects in the same room be different temperatures?
Why are some people more attractive to mosquitos?
Asked by Sarah Charles of Salisbury, Wiltshire, UK
Science is still working on the definitive answer to this Odd Body Question. Actually, mosquitoes don't bite at all, they suck the blood out of their victim. Most mosquitoes are attracted to the odour of carbon dioxide (C02). All humans exhale C02 with every breath. Yet this fact hardly helps explain why some people are "bitten" more than others.
Three early theories involving gender were proposed and then discarded. First, a theory claimed that women were more likely to be "bitten" than men because mosquitos were supposedly repelled by the strong odour of human sweat. Since the stereotyped view was that men are more likely to wash less often and be sweatier than women, so women received greater mosquito attention. But this simply wasn't true. Some men are bitten more than some women (and vice versa).
Second, a variation of this gender-based theory was that mosquitoes prefer thin-skinned people. Women generally have thinner skin than men, so women are more likely to be targeted by mosquitoes. But this too proved not to be true.
Third, it was theorised that women had some secret hormonal attractant that brought them to the attention of mosquitoes more than men. Even menstruation and ovulation could be factors in this. But such an attractant was never found. Gender does not now seem to be the all-important factor in mosquito "bite" susceptibility.
One current theory of why mosquitoes "bite" some people more than others is that diet makes one more or less attractive. Dr Randolph Morgan, director of the Insectarium at the Cincinnati Zoo, claimed that regular intake of some materials (such as yeast), which ultimately are exuded through one's pores, changes our smell and has proven effective in deterring mosquito "bites". More recent thinking is that substances in perfumes, soap residues, facial make-up, deodorants, and other compounds on the skin resulted in someone becoming more or less attractive to mosquitoes.
According to the American Mosquito Control Association of Mount Laurel, New Jersey there are over 400 such "magnetic compounds". It appears that some compounds come from within the body and some from without.
Recently, researchers have found that "masking odors" are given off by the potential victim which prevents mosquitoes from finding them.
James Logan, a research student at the Rothamsted Research in Herfordshire and Professor Jenny Mordue of the University of Aberdeen, found that "unattractive" individuals give off different chemical signals compared with "attractive" individuals. They tested the behavioural reaction of yellow fever mosquitoes to the odour of volunteers.
According to the January 2005 BBSRC Business, in one experiment, the mosquitoes were placed into a y-shaped tube and given the choice of moving upwind down one of two branches. The air flowing down one branch was laced with odour from the volunteer's hands. The other was without this odour. Their results suggest that differential attractiveness is due to compounds in unattractive individuals that switch off attraction either by acting as repellents or by masking the attractant components of human odour.
This theory differs from that of other research groups who have suggested that unattractive individuals lack the attractive components. The researchers are now testing these theories further using foil sleeping bags to collect whole body odours from volunteers.
- A mosquito can "smell" its human blood dinner from a distance of up to 50 kilometres (30 miles) away.
- A mosquito can transmit fatal diseases. Among these are Malaria, Dengue Fever, Ross River Fever, and more. At least one million people die of Malaria world wide each year.
- Mosquitoes cannot transmit HIV. The virus cannot survive in the mosquito.
- The female mosquito needs blood for protein to make her eggs. Since male mosquitoes do not make eggs, they need no blood and do not "bite".
- In 2001, the Queensland Institute of Medical Research in Brisbane, Australia, announced the results of a study of mosquito bites in identical and non-identical twins. The researchers concluded that 85 per cent of human mosquito "attractiveness" is genetic in origin.
- According to the New Jersey Mosquito Homepage maintained by Rutgers University, mosquitoes actually rely upon sugar as their main source of energy. Both male and female mosquitoes feed on plant nectar, fruit juices, and other plant liquids. Sugar is burned as a fuel for flight and must be replenished daily. Blood is needed only for egg production and is consumed less frequently.
- According to Dr Steven Schutz of the Mosquito Control Research Laboratory of the University of California at Davis, although it was once believed that blood types were an important factor in varying attraction rates, this theory has been discredited.
- Is it true that the warmer the temperature, the more likely mosquitoes will bite? Air temperature may be a factor in mosquitoes "biting", but sometimes mosquitoes prefer it cool! According to Dr Leslie Saul-Gershenz, entomology director of the San Francisco Zoological Society, the Aedes mosquito (one of the more than 3,000 mosquito species throughout the world) is attracted to humans only when the temperature is below 15°C (59°F).
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to email@example.com
No easy solution
Oh how I wish that dairy products was the answer. It's not.
I was vegan for years, and no matter where I lived in Europe (Copenhagen, Hertfordshire, Innsbruck, Malta) and no matter where I holidayed, I was always bitten more than anyone else I know.
My personal theory is that it is all about the levels of CO2 in your blood. It is a fact that blondes get more bites. They also have a higher %age of CO2 in their blood. Also, 'holy men' have said that they are more attractive to mosquitoes, and they have also a higher level of CO2 in their blood. There is research on the net about this.
The other point is that most observations are made by those who react allergically to the bites, whereas when you get used to it, you don't get a reaction. Locals in Malta say that they don't get bitten, but the truth is that they just don't show a reaction. After two years in Malta mosquito bites only produce a slight itching on me now...
Mosquitos are most attracted if you consume Dairy Products
Back in the 1990's I watched a news report on the subject of mosquito bites.. a university had been breeding mosquitos and testing the effect diet had on a persons susceptibility to being bitten. What they found was that people who had eaten dairy products where bitten numerous times while others who hadn't had any Dairy products remained unbitten or only occasionally bitten. Even in a large group the mosquitos would only single out the person who had consumed dairy products. I have observed this myself over the last 15 years, both with myself and friends. I used to be one of those people who were eaten alive if there were any mosquitos within a mile radius. I also used to consume a fair amount of milk and Dairy products. Now if I know I'm going to be anywhere that mosquito bites are likely within the next day or two I will stop drinking milk or eating Dairy Products. I now rarely get bitten, and when I do it is ALWAYS within a day of consuming dairy products. I've been out with groups of friends on dozens and dozens of occasions and without fail the people getting bitten have consumed dairy products within 24 hours and those that aren't didn't. Test it for yourself. Everybody I've told about it has found it to be true with them, they get bitten with dairy, they don't without. I used to hate the outdoors growing up because mosquitos... I owe my current enjoyment of the outdoors to the chance viewing of that newscast.
The notion of measurement of this attractiveness may be completely flawed!
The whole question about attractiveness to mosquitoes is based on the assumption that people that observe more itchy bites on themselves have been bitten more and are hence more attractive to mosquitoes. However this may be a flawed assumption!
Consider the extreme case where locals of a given mosquito-ridden region appear never to be bitten as they never have itchy red bite marks. One might assume that they are completely unattractive to the mosquitoes with 'local' blood or something.
In fact far more likely (if it has not already been proven) is that the bodies of the locals do not react to the bites in the same way having become so used to the anti-coagulants injected by the mosquitoes which are responsible for the irritation.
In the same way it may simply be that those who perceive themselves as less attractive to mosquitoes by virtue of the fact that they notice far less irritating red itchy bites may in fact just have less sensitivity to the anti-coagulants from the mosquitoes. It may be that they, as well as all the locals, get bitten just as much but just don't notice it!