2. Redness
The skin surrounding the insect bite or sting becomes red and swollen. This is an important part of the hypersensitivity reaction because it is due to an inflammatory cascade triggered by an antigen. The cells in the immune system become activated and start releasing a series of cytokines that dilate blood vessels and make your skin look red and swollen. This color is often associated with a subtle increase in temperature to the touch because the blood is flowing near the skin, and makes it a bit warmer.