What an allergic reaction to flea bites looks like. Some people are hypersensitive (extremely sensitive) to some of the chemicals found in flea saliva. This makes the bites swell up after a few minutes and form an itchy blister or hives (urticaria) that lasts for several days or weeks.

Do flea bites itch for days?

Fleas most often bite people around the legs and the ankles. The resulting red bump is an allergic reaction to flea saliva. The bites, which are usually but not always felt immediately, become increasingly irritated and may remain sore and/or itchy for as long as a week.

Why do flea bites itch so long?

Flea bites on humans appear as red, swollen bumps on skin. This is the skin's reaction to the flea's saliva. Some people are barely bothered by them, but others may have an allergy to this saliva, which can cause intense itching and painful welts.