Cradle cap, or infantile seborrheic dermatitis, is a rash seen on the scalp of young babies. It usually appears before age 3 months.
The rash consists of small, greasy "scales" and is most often seen on the scalp -- hence the term "cradle cap". Although it is often limited to the scalp, the rash can spread to the forehead, eyelids, ears, and nose, as well as down the back of the neck. In particular, I often see the "scales" under and next to eyebrow hair, as well as on the anterior (front) scalp. Seborrheic dermatitis can also appear on other parts of the body, usually in "creases" where skin folds onto itself like the base of the neck, the folds of the groin and diaper area, under the arms, inside the elbows and behind the knees. Generally the rash is not itchy; however, the skin under the rash can become red. Sometimes cracks in the skin or "weeping" (fluid exuding from the skin) can be seen, especially in skin-fold areas. Mild seborrheic dermatitis looks very much like dandruff -- in fact, dandruff is seborrheic dermatitis.
Cradle cap per se usually goes away by itself by age 8 months to 1 year, even without treatment. Some babies' cradle cap clears up in a month or so even if you don't treat it. The first step in treatment -- which works in many cases -- is to rub baby oil into the scalp. This loosens the scales, and you can then brush or comb the scales out. Leaving the baby oil on the scalp for a while before brushing can also help loosen the scales. If baby oil by itself doesn't work, many people recommend washing the scalp with any ordinary anti-dandruff shampoo, such as Head and Shoulders® (which contains zinc pyrithione) or Selsyn Blue® (which contains a selenium compound). Of course, you must take care not to let the shampoo or lather get into the baby's eyes, nose, or mouth, or anywhere else other than the scalp and hair. Some scrubbing of the scalp with the shampoo is needed to help loosen the scales. Rash in the skin folds can be relieved by keeping the skin in the folds as dry as possible (a baby powder may be helpful here). Sometimes steroid creams may be needed (for a short time) for particularly severe rashes. As always, you should check with your doctor before using any medicine on your baby, including steroid creams or even non-baby shampoos.