i used to work with a 18 yr old girl who would break out every spring and fall. her derm did all kinds of tests. he even got with her family doctor to see if there were underlying issues and couldn't come up with anything. finnally after the second year they noted it happened at the same time each year. he told her that it was like hayfever on her skin. instead of sneezing and regular allergies she would get a rash from something airborne. she started on antihistamines and creams and she was fine. when she moved away to another state she never had the rash again. we live in farm country but nothing showed up on her patch tests as an allergen. weird huh?