Her saliva contains proteins (anticoagulants) that prevent your blood from clotting. She sucks your blood into her abdomen (about 5 microliters per serving for an Aedes aegypti mosquito).

After she has bitten you, some saliva remains in the wound. The proteins from the saliva evoke an immune response from your body. The area swells (the bump around the bite area is called a wheal), and you itch, a response provoked by the saliva. Eventually, the swelling goes away, but the itch remains until your immune cells break down the saliva proteins.

Kilde: How Stuff Works om myggstikk

The diameter of a 15 min mosquito-bite weal was 10.1 +/- 10.4 mm (mean +/- s.d.) with the placebo and 5.9 +/- 5.9 mm with cetirizine treatment (P < 0.05). The 15 min pruritus scores were 36.0 +/- 25.2 and 11.2 +/- 13.2 (P < 0.001), respectively. The diameter of the 24 hr mosquito-bite lesion was 12.6 +/- 21.9 mm with the placebo and 7.4 +/- 16.1 mm with cetirizine treatment (P < 0.01).

Kilde: National Library of Medicine om cetirizine

PS! Cetirizine er virkemiddelet i allergimedisinen Zyrtec