My husband has had this for over 2 months now and no one has been able to find out why. He finally went to an allergist recently and is going through a blood test now to see if there is anything there, then it will be on to an allergy test. I think its been called Uticaria. There's alot of info online about it and no real reason people get it and no solution to the problem....it just goes away on its on basically.
I have. The same type of issue, I've been told stress, or an allergic reaction.
It could be a scratch mark! If not hives, it could be dermatitis, perhaps a mite infection such as scabies, eczema. He should probably visit a dermatologist and simply be diagnosed and treated - the sooner the better regardless of what it is that's ailing him. It's best to take care of these things as quickly as possible to minimize any further damage to the skin.