Why are some people more likely to have them?

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Relaxing outside on a summer evening, what could be better? Then someone gets bitten by a mosquito and the assault begins. While mosquitoes feast on their chosen targets, others escape unscathed – but why? Medical News Today looks at what attracts mosquitoes, why they target certain people, and how to try to stop them biting if you’re one of the unlucky ones.

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Why do some people always seem to be victims of mosquito bites? Image credit: Wizemark/Stocksy.

There is more than 3,500 kinds mosquitoes, only some of which bite people. And it’s only female mosquitoes that bite – they need blood as a source of protein for their eggs.

To obtain it, they puncture the skin of their chosen host with their needle-like proboscis, resulting in a bite that can itch, swell and even cause serious illness.

In many countries, a mosquito bite is more than just an annoyance. of the malaria parasite transmitted by the Anopheles species to the viruses that cause yellow fever and dengue fever, mosquitoes are responsible for transmitting many of our greatest killers.

Even if you live in a place where a bite poses no risk of disease, the high-pitched whine of a mosquito is an unwelcome noise.

The itching and swelling from a bite can last for several days. Scratching the itch can lead to infection and, for very few people, an allergic reaction that can lead to anaphylactic shock.

How many times have you returned from an evening barbecue or camping trip covered in mosquito bites to find that others on the same outing weren’t bitten at all? What makes mosquitoes feast on some people while seemingly ignoring others?

Dr. Jagdish Khubchandani, professor of public health at New Mexico State University, said Medical News Today this:

“The reasons why mosquitoes are attracted to humans have been discussed in a few studies. These studies looked at body odor, body color, skin temperature and texture, microbes living on the skin, pregnancy status, carbon dioxide exhaled by humans, alcohol and type of diet. Overall, studies suggest that pregnant women, people with high body temperature and sweating, a diverse presence of skin microbes, and those with darker skin may be more susceptible.

But the answer is not simple: chemicals that attract some species of mosquitoes have been shown to repel others. And people produce thousands of different chemicals, so determining which ones affect mosquito behavior is far from easy.

Humans, like almost all other animals, give off carbon dioxide (CO2), heat and moisture due to cellular respiration. And this is what initially attracts mosquitoes.

Female mosquitoes detect CO2, as well as other odorants for human skinusing highly sensitive nerve cells called cpA neurons.

A study suggests that three different species of disease-carrying mosquitoes are activated and attracted to CO2. But everyone exhales CO2, so that can’t explain why mosquitoes bite some people more than others.

Another study suggests that the higher the CO2 production, the greater the attraction. “Individuals with greater body mass appear to be more attractive to mosquitoes and midges, which may be related to other characteristics such as increased surface area and CO2 production,” its authors write.

So, could maintaining a healthy body mass help deter biters? It remains unclear.

Several studies have identified lactic acid as another chemical that mosquitoes are attracted to. As early as 1968, a study found that lactic acid attracted female yellow fever mosquitoes.

Another called it a signature human odorant for mosquitoes.

We produce lactic acid when we exercise, so the best advice is to wash with soap soon after exercise. Then, dry yourself thoroughly before leaving.

We are covered in millions of bacteria — the skin microbiota — which are vital for keep our skin healthy. But does the composition of your skin microbiota determine whether we are susceptible to getting bitten or not?

A study studied this with Anopheles gambiae, a species that carries malaria. They first tested the skin microbiota of 48 men before using glass marbles rolled on the men’s feet as bait in mosquito traps.

They found that nine of the men were highly attractive to mosquitoes, seven were unattractive, with the rest falling in between.

And did the microbiota have an effect? Apparently yes. The higher the number of bacteria on the feet, the more they attract mosquitoes.

But, the study concludes,[i]individuals with greater microbial diversity […] are less attractive to mosquitoes and therefore may receive fewer bites.

Our skin microbiota is influenced by our genetics, our age and our immune system, which we really can’t do much about. But the products you use cleaning and moisturizing it can also have an effect, so maybe avoid antibacterial soaps if you want to try and keep the bugs from biting.

These helpful microbes also affect the chemicals we give off. Human sweat, for example, is completely odorless until bacteria act on it.

All of these skin bacteria convert compounds in our sweat and sebum into volatile compounds, some of which attract and others repel mosquitoes.

And, according to the study above, certain skin microbiota appear to release compounds that make people less attractive to mosquitoes and therefore function as a built-in defense system.

Unfortunately, we have yet to figure out how to manipulate the skin microbiota to harness these beneficial effects, but the study authors believe their findings may provide some insight.

“Discovering the link between skin microbial populations and mosquito attraction could lead to the development of new mosquito attractants and personalized methods of protection against vectors of malaria and other infectious diseases,” note- they.

In sebum, one study suggests that two saturated fatty aldehydes — decanal and undecanal — are odorous substances that attract mosquitoes. The composition of sebum and levels of long-chain aldehydes vary from person to person. Could this be another reason for selective biting?

More … than a study studied whether blood type had an effect on the likelihood of you being bitten. This is good news for people with blood type A – mosquitoes seem to find it less appealing – but not so good for blood type O.

People with this blood type were considered a tasty meal by almost twice as many mosquitoes as those with type A.

There is, however, a compensation for people with blood group O. If the mosquito that bites you carries the malaria parasite, people with blood group O are much less likely contract severe malaria than people with other blood groups.

Another theory is that everyone gets bitten, but some people just don’t notice the bites because they don’t react.

If there’s no itching or swelling, maybe they’re just assuming they haven’t been bitten.

Dr Khubchandani agreed there might be something to this theory: “Anyone can be bitten by a mosquito, but our reactions may differ. It partly depends on the type of mosquito bite/species, our immune system and our personality and behavior – whether we eliminate it or take the bite seriously.

So if you’re one of those people that mosquitoes love to feast on, scientists still can’t tell you exactly why. Maybe you are giving off more CO2, heat, or lactic acid, are blood type O, or have the “wrong” type of bacteria in your microbiome.

But don’t just accept your fate. There are steps we can take to help prevent mosquitoes from biting us.

One measure might be to wear light-coloured clothing, such as some studies suggest that mosquitoes are attracted to dark colors. Light greens and blues may be best – as far back as 1902, a study suggested that orange and yellow seemed to repel insects.

Use insect repellent on the skin – natural products, such as citronella, citronella and mint, can be effective if a person doesn’t feel like covering themselves with DEET.

Maybe avoid beer — a small study found that people who drank beer were significantly more attractive to mosquitoes.

If you have a garden, make sure there is no standing water in which mosquitoes can breed.

Also check your garden planting – strongly scented plants such as basil, lavender, lemon thyme and marigolds may smell good to us, but mosquitoes will stay away.

And if all else fails, sit next to someone who’s even more of a bug magnet than you!

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