My little brother got a mosquito bite the other day. it seems to have burst a blood vessel in his right forearm. after a day, there is now a 2 inch blue blotch. it doesn't cause him pain unless he applies pressure to it. it's this cause for alarm?

No cause for worry unless there is worsening pain, growth, or active bleeding.

An application of a cool pack and topical antihistamine lotion is often effective. Watch for signs of fever, increase in swelling and drainage.

If you are describing a “bruise” or dry blood. Moist heat with mild message will help in breaking it up and being absorbed by the body. If skin not broken very little risk of infection