My husband just finished five weeks of radiation therapy for a solitary plasmacytoma in the ball of his left humerus. He handled the therapy well with only some fatigue. The skin on the back of his shoulder, however, is now darker than the rest of his skin (which is to be expected) but it is also speckled with very many small black dots. They look almost like blackheads but they are smooth like freckles except the skin is a little rough. Under his arm, he has more of the dots but they are like skin tabs, larger, and raised from the skin. They are also quite irritating. Can you explain what kind of reaction this is, should we be concerned, and how should he treat it?