Bruising after being bitten by mosquitoes may be caused by anaphylactic purpura, scratching and so on. In the mild case, you can use soap and water, and in the severe case, you should seek medical attention as soon as possible.
First of all, the mosquito bite will not appear bruising, bruising is caused by subcutaneous bleeding, and cause subcutaneous bleeding may be due to mosquito bites caused by an allergic reaction, allergic reaction is mildly manifested as itching, red papules and so on.
Allergic reaction is mild, manifested as itching, red pimples, etc. Allergic reaction is intense, or excessive scratching will make the capillary permeability increase, capillary rupture, blood cells outflow silt in the subcutaneous, which is manifested as bruises, also known as purpura.
Mosquito bites should try to avoid scratching, you can use soap and water rinse, spray mosquito repellent, etc., allergic reaction symptoms should be treated as soon as possible to the hospital.