Large doses of almost any drug over a very long period of time can result in what I found out was a Fixed Drug Reaction. It can show up as hives, a rash, or open sores, but they are usually on moist areas of the body. I stopped taking the medication I used and the reactions stopped.
And I had many incidents of giant hives from something in my 20's and the swelling in my throat nearly blocked my airway once. Yes hives can be deadly. I suggest stopping the use of Proactive, and have it allergy tested on you by a doctor. Or just find another product.