Can one be ‘allergic’ to mosquito bites?

The warm, rainy weather over the last few weeks has provided the ideal breeding conditions for mosquitoes. As a result, their numbers are increasing in many regions across Germany. For most people, mosquito bites are a harmless nuisance. But in certain individuals, large hives can develop on the skin where they have been bitten. Do these reactions indicate an allergy? ECARF spoke about this with Marcus Maurer, Professor of Dermatological Allergology at Charité Berlin.

There is an audible buzzing nearby. The female mosquito lands, pierces the victim’s skin with her proboscis, and sucks out the blood. She needs this blood meal to develop new eggs. Once the mosquito has had her fill, the victim is left with inflamed, itchy skin. That’s because whenever a mosquito bites, it releases some saliva, which contains proteins that prevent clotting, dilate the blood vessels, and make it easier for the mosquito suck in the blood. At the same time, the proteins activate the mast cells, a type of immune cell that releases the neurotransmitter histamine, which sets off the uncomfortable itching and inflammation.

Prof. Marcus Maurer
Prof. Dr. Marcus Maurer

According to Marcus Maurer, Professor of Dermatological Allergology at Charité Berlin, ist die Reaktion zwar unangenehm, aber auch nützlich, „

the reaction may be unpleasant but it is also useful. “Over the course of evolution, the human body has learned that insect bites can lead to infections. It makes absolute sense to have defence cells at the site of the attack.”

It is normal for a one-centimetre hive to appear after being bitten. However, some people develop more extensive swelling at the site of the bite. They often believe this to be an allergic reaction to the mosquito bite. It seems to make sense – after all, these reactions commonly occur after bee and wasp stings. But is there a true ‘mosquito bite allergy’?

Anaphylaktische Reaktionen sind die Ausnahme

For this to be a true allergy, the immune system would need to develop antibodies (immunoglobulin E) against the proteins in the mosquito saliva, which are harmless in themselves. But this kind of reaction only occurs in rare cases after a mosquito bite, says Maurer. Although there are no conclusive studies on the prevalence of allergies to mosquito saliva, we do know that their significance has been overshadowed by bee and wasp venom allergies.

Furthermore, it is difficult to prove such an allergy. Up until now, only a few allergens in mosquito saliva have been identified and made available for test preparations. But if an allergy is actually present, it must have an effect not just on the skin but the entire body. “This could lead to nausea, difficulty breathing, rapid heartbeat and circulatory collapse due to an anaphylactic reaction”, explains Maurer. “We have one patient who went into anaphylactic shock twice from mastocytosis and a mosquito bite allergy. But it was an exceptional case. This sort of thing is seen more frequently at the bigger allergy centres.” Note: Mastocytosis is a rare disease in which a large number of mast cells accumulate in the skin. Anaphylactic reactions are often more severe in individuals with mastocytosis.

In most cases, severe swelling after a mosquito bite is due to inflammation rather than an allergy. However, it is unclear why some people have such extreme reactions. Environmental toxins or high levels of protein in the saliva of the mosquito are often blamed. But according to Maurer, these are merely assumptions with no supporting evidence.

Advice: slap, don’t scratch

Cortisone ointments may be used to treat these areas of inflammation, which can become as big as the palm of a hand. If there are many large bites, a short course of antihistamines or oral cortisone may be prescribed. The site of the bite is often infected by bacteria, which can be treated with antibiotics. Since scratching the itchy skin may promote bacterial infections, it is best not to scratch. But itchy hives are hard to ignore. The allergist suggests that “rather than scratching the skin, it is better to slap the spot where it itches. This is what people do in Asia. You can also rub it with your fingertips, although even this is an additional mechanical stimulus that is more pro-inflammatory than anti-inflammatory.”

Maurer does not endorse home remedies for itching such as cut onions or aloe vera. Instead, he prefers to use cooling or heating devices. Cooling the itchy skin with a gel pack slows down certain inflammatory processes and encourages the itching to move along the nerve pathways. However, cooling is most effective while it is being applied.

A brief application of heat could have a longer-lasting effect. A battery-operated pen delivering heat at a temperature of approximately 50ºC is held against the mosquito bite for a few seconds (Maurer advises not to use a heated spoon or coin due to burn risk). The heat may effectively reduce symptoms. “We used to think that the substances in the saliva were being destroyed, but this is unlikely (…) We do know that the nerves in the skin are very sensitive to overheating, so they turn off the stimulus conduction and the itching signal is no longer transmitted to the brain.”

So ice packs and thermal pens might come in handy this summer. The best scenario of course is not to get bitten in the first place. Wearing light-coloured clothing that covers as much of the skin as possible and using mosquito nets are effective ways to repel mosquitoes. Using a mosquito repellent on top of that is your best bet for remaining well protected during the mosquito boom this year.