Why Do Mosquito Bites Itch?

By: Tova Goldstein  |  October 2, 2016


With all of the talk of the Zika virus in recent headlines, mosquitoes have gotten quite a bad reputation. While not all mosquitoes carry Zika, no one likes encountering these pesky little menaces. We have all enjoyed a nice day outside only to have it suddenly spoiled by an itchy red welt rising up on our skin. Without always seeing the insect, we immediately cast the blame as we try to contain the urge to scratch. But what is it about mosquito bites that make them so itchy?


Mosquitoes use their proboscis, straw-like mouths, to pierce the skin and draw blood. Only female mosquitoes, requiring blood nutrients to produce their eggs, bite. Once the skin is pierced, the mosquito injects its saliva into the blood. The saliva contains an anticoagulant, a substance which works to prevent blood clotting, which ensures that the blood will not clot around the mosquito’s proboscis, trapping it in the skin.


Like other foreign materials which enter the body, the mosquito’s saliva is recognized by the body’s immune system as a foreign pathogen, initiating an immune system attack and releasing histamine. Histamine, an organic nitrogenous compound, is involved in the body’s natural inflammatory response and in pruritus, the sensation which causes the desire to scratch. Histamine is produced by basophils and mast cells, immune cells located in nearby connective tissues. The histamine aids in increasing the blood capillaries’ permeability to some proteins and white blood cells, which grants them access and allows for them to encounter the pathogen in the infected tissues. The histamine reaction causes the itching as well as the swollen and enlarged blood vessels, thereby causing the raised bump at the site of the bite.


Dr. Jonathan Day, a professor of medical entomology at the University of Florida in Vero Beach, explains that not everyone reacts to mosquitoes with a red swollen bump. Instead, he explains that some adults do not notice when they have been bitten, and that over time many adults actually develop a tolerance to mosquito bites. Most adults tolerate the mosquitoes near their home, reacting less severely than they did when they were younger. However, if they travel and encounter new mosquito species they will react severely, in a manner similar to when they were children. Additionally, according to Nanette Silverberg, director of pediatric dermatology at St. Luke’s-Roosevelt Hospital Center in New York, different people have different allergic reactions to mosquito saliva; some reactions are simply stronger than others. Therefore, while you might be full of itchy red welts, your friends and family may get bitten and hardly even notice.


Let’s say that you have been bitten: what do you do? Scratching at the bite is never advised as it starts a vicious cycle; scratching releases more histamine which only makes the itching worse. Instead, over the counter anti-histamine and cortisone creams could reduce the itching and lessen the inflammation. Furthermore, taking allergy medication before you are bitten may aid in preventing the allergic reaction from happening. Despite popular opinion, calamine lotion does not have anti-itch properties. Yet, due to its soothing pink color, calamine lotion has a psychological soothing effect, similar to a ‘placebo-effect.’ Although there is no concrete scientific support for the effectiveness of certain well-known home remedies, it is unlikely that applying ice, honey, garlic, a paste of water and baking soda, or the like will cause any harm.