Why Do Mosquito Bites Swell Up So Much?

Medically Reviewed

Besides being itchy and uncomfortable, mosquito bites can cause an uncommon allergic reaction that translates into the bites morphing into large, swollen hives.

This reaction is sometimes called “skeeter syndrome” and occurs more often in people with immune system disorders and children who haven’t yet developed an immune response against mosquito bites.

It can also occur when you’re bitten by a mosquito species you’ve never been exposed to. If you have skeeter syndrome and know you’ll be in an area where you’ll be exposed to mosquitoes, ask your doctor if you should take a nondrowsy antihistamine to ward off any reactions.

But, first, you want to be sure your welts are triggered by a bite — not by scratching the itch. If the redness and welts first appear hours after a mosquito bite, you may have infected the area by scratching and breaking the skin. If swelling, redness, or warmth persists, see your doctor, since it can lead to bacterial cellulitis, a potentially serious condition.

Apply an ice pack first

For relief of non-infected bites, elevate the afflicted area and hold an ice pack against the welts. Apply an over-the-counter itch-relief cream, and consider an oral antihistamine. If those strategies don’t do the trick, talk to your doctor about getting a prescription for a topical steroid to mute the reaction.

Otherwise, your best bet is prevention. Try to avoid being outside from dusk to dawn, when mosquitoes are most active. If you’re outside during the day, move away from standing water, where the insects breed, and shady, humid spots. Forgo your favorite cologne and dress in darker colors — scents and bright hues attract mosquitoes.

What to spray on for prevention

And no matter the hour, if you’re outside you should apply insect repellent that contains DEET, picaridin, oil of lemon eucalyptus, or IR3535. Products with less than 10 percent of an active ingredient may offer protection for just one or two hours, according to the Centers for Disease Control and Prevention. Concentrations of DEET above 50 percent do not offer a big increase in protection time, the CDC adds.

Look for an EPA registration number (EPA Reg. No.) on the label. The CDC recommends the use of products registered by EPA. Remember to test products on a small patch of skin before applying them to your entire body, as they can cause allergic reactions.

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Why Mosquitoes Bite

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