My 15 year old son went for a bike ride today, 3 degrees outside and his lower legs were very wet and cold from crossing through a river. He came in and took a hot showers as he was freezing. Upon coming out of the shower, his ankles and feet where mottled re and white with very itchy swollen hives. I covered them with Benadryl cream and l Also gave him an oral Benadryl ....is this serious.? And why did this occur so suddenly. He has done this before and never had a problem. He had the flu about 10 days ago ( high fevers, headaches, body aches). But is fully recovered.