I used to get hive and welts once every 10 yrs for 3 months at a time. No clue what caused it. Nothing helped. Well almost 15 yrs ago I had radiation to get rid of my thyroid and have not had a hive or welt since. Doctors think that because I had an overactive thyroid that everything is elevated in your system and thought that what ever caused the hives were exgerated because of hyperthroidism. Good luck, hives are miserable.