What Could Blister On The Back Of A Leg Be From?

When an insect bites, such as a mosquito for example, it usually injects an anaesthetic under the skin so that you can't actually feel it bite. This then swells up and has the similar appearance to blisters. 8 blisters on the back of the thigh, sounds to me more likely to be resulting from insect bites.

I get hives all the time but I had a friend in High school who used to get a sort of blister on the inside bend of her elbow when she had allergies.  They were painful for her and I don't know how she ever got rid of them but I know she did see a dermatologist a few times.
I doubt that helped, but...
Auntimaime-