It sounds like Solar Urticaria,or hives and its all too common, triggered by an allergon perhaps and exacerbated by the Sun, keep him out of the direct rays of the sun, there are cortisone creams may work for some and Antihistimines,it could be he is allergic to your Dete rgent there is a free and clear one to use.but he could be allergic to a number of things. Try cutting out differant foods and hair products and shower Gels,and just see if it .helps, its a tough one as there are so many things out there that affect our skin, seek help from a dermatologist .