UW Today

August 2, 2011

When mosquitoes bite, take antihistamines for relief

UW Health Sciences/UW Medicine

In the warmer summer months, mosquitoes are unwelcome companions during many outdoor activities. While most people only have mild reactions to their bites, people with allergic reactions can experience severe symptoms. Recently I saw a 4-year-old boy during a clinic visit. Every time, he would get bitten, the affected body part would swell to nearly three inches across. Due to his scratching and congestion from the swelling, he had multiple episodes of cellulitis, a potentially serious bacterial skin infection that required antibiotics to resolve.

A female mosquito alights on a hand.

A female mosquito alights on a hand.CDC

If you or your children suffer from these reactions, oral antihistamines are a powerful, but sometimes overlooked, home treatment. They are much more effective at relieving swelling and itching than topical products (including topical antihistamines and calamine lotion). For best relief, I encourage patients with mosquito bite sensitivities to begin taking an antihistamine a few hours before going into an area where they are likely to be bitten. Depending on the size of the reaction, it may be necessary to repeat the recommended dose for a few days until the swelling subsides.

Many antihistamines are now available over the counter. Since they are similar in effectiveness, your choice of product can depend on brand preferences and tolerance for side effects. From most to least sedating, these products include diphenhydramine (Benadryl)), cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra). Keep in mind that Benadryl must be taken every six hours to be effective. The other products provide 24-hour relief.

With antihistamines, you should be able to treat most mosquito bite reactions at home. Ice can also help to reduce local swelling, if applied shortly after being bitten. To prevent infections, try not to scratch itchy bites. Scratching can result in open sores, which increases the risk of developing staph (Staphylococcus aureus), strep (Streptococcus pyogenes) and other bacterial infections. Watch for any of the following warning signs, which should be evaluated by your healthcare professional: Your swelling does not start resolving after a day of antihistamine treatment; you have open sores at the bite sites; or you have infections involving your eyes or joints.

Dusk on a lake, a prime time and location for mosquito bites.

Dusk on a lake, a prime time and location for mosquito bites.Allison Gray

Mosquitoes are typically most active at dawn and dusk. Some species are also day biters, including the Asian tiger mosquito, which can carry the West Nile Virus. For this reason, whenever you are outdoors, the best protection is a long-sleeve shirt, long pants and a hat. You should also use a mosquito repellent if you are hiking or camping in woods and wetlands. Many repellents include DEET as the active ingredient. They should be applied carefully by following the instructions for adults and children on the label.

Delilah Warrick, M.D., is a board-certified family medicine doctor at the UW Neighborhood Clinic in Kent/Des Moines. For more information, call 800.852.8546 or visit www.uwmedicine.org/uwpn.