If you venture forth at dusk with arms or legs uncovered, you may get chewed up by hungry mosquitoes. When prevention doesn't work, you end up with itchy, swelling welts resulting from the bites. Preventing bites is your first line of defense. Limit your exposure by covering up as much as possible, staying indoors at dusk and avoiding breeding grounds near stagnant water.
Cover the affected area with a cool, wet washcloth or better yet, ice cubes in a zip-top plastic bag and wrapped a small towel or an ice pack designed for athletic injuries or aches.
Rub in diphenhydramine cream, sold as Benadryl, to calm the bitten area. Reapply when the area starts to itch again. Use generic Benadryl creams to save money -- the active ingredients are identical to the trademarked cream. Or take Benadryl internally if the potential side effect of drowsiness is not a concern.
Apply a thin layer of a steroid cream such as hydrocortisone to the affected area. Follow the directions on the tube regarding how many times to apply per day.