Scabies is a skin irritation caused by an infestation of tiny parasitic mites that burrow under the skin. The bumpy rash you see is actually an allergic reaction to the eggs and feces the mites leave behind. The name comes from a Latin word meaning "to scratch," and if your baby has scabies, he's likely to be doing lots of that.
Your baby can contract scabies through skin-to-skin contact with someone who has it. Scabies is extremely contagious, and anyone can get it — even if they're scrupulously clean. It often shows up in more than one family member or in groups of children in daycare. There's no particular time of year when scabies is more prevalent.