Skin Rashes, Blotches Like Dry Skin, Painful And Sore. Why Has It Been Persistent?

my partner has a skin rash. He's had a blotch of what looked like dry skin on his left hand for about 2 months. He now has a red blotchy dry looking rash on the inside of hid thighs and the inside of his elbows for about 2 weeks. His right elbow has now broken out and is weeping and raw looking and painfulll. At first we thought it might have been a reaction to the brand of washing powder, but it has been changed since (before the sore appeared) and the rash persists. We have tried rolling a glass over the rash and it dissapears, we cant see any marks where a mite might have gone under the skin. To be honest it looks like hives but its the wound that has broken out on his right elbow that is causing us the most consern.