Hi,
Hives are caused by inflammation in the skin and can be triggered when certain cells in the body release histamine and other chemicals into your bloodstream and skin. This may be caused by allergic reactions to medications or foods or other allergens.Additional triggers include physical factors such as environmental factors ( heat, cold, sunlight, water, pressure on the skin, emotional stress and exercise). Preventing the triggers will help prevent the symptoms. Anti-histamine medications may also help.
Take care and regards.
i also have this problem, i get hives all over my body when i exercise, get out of the shower, go swimming or even run.ive noticed for some reason they seem worse or appear faster in the heat, so maybe that could be the problem.but im not sure i have had it for 8 yrs now and i have no insurance to get a doctors perspective.