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ACAAI > Patients & Public > Resources > Ask the Allergist

Scarring from mosquito bites?

Q. I had a few questions about my reactions to mosquitoes. I am 11 years old and whenever I get a mosquito bite, it either swells up the length of my thigh or turns into a big blister. These blisters then become black circular scars which (as you would imagine) are not the most attractive thing in the world! Is this considered a severe reaction? Any suggestions would be great.

A. Indeed, you are having a severe reaction to mosquito bites. The substances causing the reaction are the proteins in the mosquito’s saliva that they inject when they bite you. Typically when anyone is exposed to a particular type of biting insect, they go through a well described series of responses. At first, there may be no response to the bite. After more bites, the immediate immune response begins, characterized by itching and redness shortly after a bite. Hours later, the immune response may continue and swelling could increase (called a delayed response). Eventually, a person can lose the delayed response, and ultimately even the immediate one, in time. The timing of this series of responses is dependent on many factors but most importantly how often one is being bitten, and it may take several years to progress through all the stages to no longer being sensitive.

Some people have a more severe reaction that involves worse swelling that may take 3-10 days to resolve. Sometimes there is bruising or blistering as you describe. Very rarely individuals may have systemic or generalized symptoms, away from the site of the bite. This reaction has been termed Skeeter Syndorme by my colleague Dr Estelle Simons. The good news with this is that the reaction usually gets better over time, but the bad news is that there is no specific therapy that will speed this along. Consequently we are left with avoidance and treatment with antihistamines. Avoidance includes not going to areas with a lot of mosquitoes (especially at dawn and dusk when mosquitos are most active), using permethrin (an insecticide available at outdoor stores) treated clothes and insect repellents like DEET (a commercially available insecticide that can be applied to skin) to keep mosquitoes away from you. After being bitten, a long acting antihistamine like cetirizine, fexofenadine or loratadine may minimize the reaction. These are all available over the counter. One word of caution is that because of scratching, the skin around the bite area may become infected. Skin infection causes the area to be red, swollen, warm and painful. This can look just like the large local reaction you describe, but typically occurs later. So if the reaction seems delayed or if it keeps getting worse after a few days then you should see a local doctor to check for the possibility of infection.