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Why does a mosquito bite itch?


Itching at the site of a mosquito bite is the body’s reaction to the saliva that the insect injects into the skin.

When it bites, it pierces the skin with a special proboscis. At the same time, through one of its tubes, which is called a large lip, the mosquito feeds, that is, it drinks blood, and through the other – the hypopharynx , injects saliva.

Saliva contains an anticoagulant – that is, a substance that prevents blood from clotting. If the blood clots around the mosquito’s mouth, it can get stuck in the host’s body and not fly up after it finishes eating.

In addition to anticoagulants, mosquito saliva contains 19 other enzymes and proteins. They are foreign to our body. Therefore, when they get inside, the immune system reacts to them as a threat. What happens next, according to classical ideas, resembles an allergic reaction.


According to some scientists, sensitivity to mosquito bites in humans occurs after they have been bitten for the first time. Due to such sensitization, in the future, with each bite, the body secretes special immunoglobulins, which lead to the destruction of the mast cells of the immune system. On the one hand, they help to heal wounds and protect against pathogens, but on the other hand, they release histamine. The release of this substance causes itching.

However, today there are new studies that suggest that in fact the whole mechanism of reaction to mosquito bites can be somewhat more complicated and does not depend on mast cells and histamine or depends on more than just them. It is assumed that substances other than histamines are released, which then cause peripheral neurons to signal to the central nervous system. It interprets these signals and sends the information to the brain so that the brain lets you know that the mosquito bite is itchy.

By the way, only female mosquitoes bite. The fact is that the blood contains the nutrients that they need to lay eggs. Males do not need to do this, so they do not bite either people or animals. They feed on plant sap.


Some people have only a mild reaction to a mosquito bite or bites. Other people react more strongly. Consequently, a large area of edema, soreness and redness may occur at the puncture site.

Signs of a reaction to a mosquito bite include:

  • a swollen red bump that appeared a few minutes after the bite,
  • a hard, itchy, reddish-brown bump or bumps that appear about a day after the bite or bites
  • dark spots that look like bruises.

However, in children and adults who have been bitten by mosquitoes in the past, and in people with weakened immune systems, the reaction may be more severe. Also, a mosquito bite on the inside of the forearm is more difficult to tolerate.

In these cases, a person may experience:

  • a significant swollen area at the site of the bite,
  • elevated body temperature,
  • hives,
  • swollen lymph nodes.


Some people develop a very severe allergic reaction to mosquito bites. Their bite can cause anaphylactic shock. Its symptoms are:

  • breathing problems
  • laryngeal edema
  • swelling of the face
  • hives
  • weakness
  • loss of consciousness.

If a person develops anaphylactic shock, they need emergency medical attention. This is usually an injection of adrenaline, specifically via auto -injectors .


In general, redness and swelling at the site of a mosquito bite can last from several hours to several days. Each person reacts to mosquito bites in their own way. The main thing is not to comb or scratch the bite site, because this can lead to longer wound healing and even infection.

Sometimes small dark marks remain at the site of mosquito bites long after the itching and the bite itself disappear. As a rule, they occur in people with sensitive skin. However, these traces must pass. To avoid hyperpigmentation at the site of a mosquito bite, creams with vitamins C, E or niacinamide can be applied .


The best way to prevent mosquito bites is to prevent them. But here it is important to know what exactly needs to be avoided, and what, on the contrary, can scare away these insects.

To protect yourself from bites, treat your clothing with mosquito repellent solutions or sprays, and wear long-sleeved shirts and long trousers.

Try showering or using an antiperspirant. Sweat and body odor attract mosquitoes.

Drinking alcohol has also been found to be associated with a greater likelihood of being bitten.

If you live in a private home, to reduce the number of mosquitoes, get rid of stagnant water, open drains, empty children’s pools at least once a week, change the water in birdbaths at least once a week, get rid of old tires and empty flower pots regularly or store them upside down…

When traveling to other countries, you need to remember that mosquitoes can carry diseases such as West Nile fever, Dengue fever, filaria parasitic worms, malaria, etc.

A recent report from the US Centers for Disease Control and Prevention found that the number of diseases transmitted by mosquitoes and other arthropods, including bed bugs, has more than tripled since 2004.

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