Despite the term, mosquitoes don’t actually bite. They pierce the skin to get at the blood just beneath it. That red, itchy bump that appears is the body’s allergic reaction, and not the result of a tiny wound.
The way it works is that a mosquito uses heat sensors on its antennae and around its mouthparts to locate capillaries near the skin’s surface. The mosquito has a proboscis – a long, pointed mouthpart – and inserts that to tap the capillary.
There are two tubes in the proboscis. The mosquito uses one to inject saliva, while the other draws in blood. The saliva contains enzymes that serve two purposes: act as a mild painkiller, so the prey doesn’t notice, and thin the blood so that it does not clot and keeps flowing.
When the human body detects these enzymes, it reacts as if they are foreign invaders similar to viruses or illness-causing bacteria. Antibodies trigger the production of histamine, which is released from the mast cells.
Histamine moves the site of the bite and binds to receptors, causing the blood vessels in the area to dilate. The increased blood flow brings in more white blood cells to help fight the invader, or antigen. The body might release too much histamine, and that makes the spot swell and become itchy.
The resulting bump is called a “wheal.”
Each person’s allergic reaction to a mosquito bite varies. Some people actually become relatively immune to them with repeated exposure, while others become even more sensitive. Children are especially vulnerable to allergic reactions to mosquito bites.
Rarely, a person will have a severe reaction that causes major swelling, or even experience anaphylaxis, a dangerous condition that threatens to restrict breathing.
There are various treatments to help reduce the swelling and itching from a mosquito bite. They include:
- Calamine lotion or Caladryl – A combination of zinc and iron oxides reported to have a soothing effect on itchy skin. Caladryl also contains a mild topical analgesic for pain.
- Icepacks – The cold constricts the blood vessels, which helps reduce the swelling, and numbs the skin to lessen the discomfort.
- Ibuprofen or hydrocortisone cream – Both will work to reduce swelling, and hydrocortisone also is widely used to soothe itching.
- Anti-histamines – An over-the-counter medication such as Benadryl can counter the effects of the histamines, blocking them from binding to receptors so the itching subsides and the blood vessels return to normal.
Scratching is never a good idea, no matter how good it feels. The itch won’t go away, and the scratching will just break the skin, making for more itching. It’s best just to wash with soap and run cool water over the bite.
In most people, mosquito bites should last no more than about 24 hours.
Learn more about Mosquito Bites.