Why do mosquito bites become large red lumps under the skin after scratching?

Mosquito bites don't actually become large red lumps under the skin after scratching, but rather they swell up and become red on the skin. This is due to a combination of factors:

1. Initial Reaction:

* When a mosquito bites, it injects saliva containing an anticoagulant (to keep the blood flowing) and other proteins.

* Your immune system recognizes these proteins as foreign substances and launches an immune response.

* This response causes localized inflammation, leading to redness, swelling, and itching.

2. Scratching:

* Scratching the bite introduces bacteria from your fingers into the wound.

* This further irritates the skin and leads to an even stronger immune response.

* The immune system releases histamine and other inflammatory chemicals to fight off the bacteria.

* These chemicals cause more swelling, redness, and itching, leading to the characteristic "large red lumps."

3. Other Factors:

* Individual Sensitivity: Some people are more sensitive to mosquito bites than others, leading to a stronger reaction.

* Bite Location: Bites on certain areas of the body (like the face or neck) tend to be more sensitive.

* Secondary Infection: If the scratched bite becomes infected, the swelling and redness will be even more pronounced.

In summary, the large red lumps after scratching a mosquito bite are a combination of the initial immune response to the saliva, the irritation caused by scratching, and potentially a secondary infection.