I'm a 22-year-old female. About a month ago I got a patch of hives, seemingly from resting a plastic folder on my knee (a folder I'd been carrying daily for months). Since then, I've sporadically gotten more, once from that folder again on my arm, twice from the waistbands of synthetic underwears, once from an upholstered chair in my house that I'd sat on daily with no problem, and once from a certain synthetic fabric bra with no reaction until afternoon.
So it seems to be related to synthetic materials, perhaps combined with sweat or moisture. None of the clothing was new, and it was all just washed. No new detergent or body wash, no eating differently, no living anywhere new. I moved to China in January 2014, traveling weekly between Hong Kong and Shenzhen, and it's happened in both places. Both are polluted and humid, pretty much constantly 90 degrees May through September, but as I said, I had no hives until this August. I did get bitten by bedbugs one night around a month ago if that's somehow related.
So I'm wondering, why might my skin be suddenly and sporadically reacting to so many things? Can I make it stop?