Friction rash. This is the most common form of diaper rash, and affects almost all babies at some time. It is most common on areas where friction is most pronounced, such as the inner thighs, or under the elastic of diapers that are too tight. It comes and goes quickly, and responds well to frequent diaper changes, airing out, and protective barriers.

Irritant rash. This is most conspicuous on the exposed areas, such as the round part of the buttocks. It tends to spare skin folds and creases. It's generally the result of contact with stool enzymes or irritants such as harsh soaps, baby wipes, detergents, or topical medicines.

Allergic rash (contact dermatitis). This may occur in combination with an irritant rash or by itself. It is also more common on exposed areas. The skin looks like poison oak.

Intertrigo. Moist heat causes this common type of diaper rash that occurs deep in the skin folds. The involved skin looks thin, as if it has lost several layers. Seborrhea rash. A salmon-colored, greasy rash with yellowish scales characterizes this diaper rash that is also worse in the skin folds.

Psoriasis. This stubborn rash doesn't necessarily look distinctive. Other signs of psoriasis usually accompany the diaper rash, though, such as pitting of the nails or dark red areas with sharp borders and fine silvery scales on the trunk, face, or scalp.

A number of rare diseases such as congenital syphilis, histiocytosis X, zinc deficiency, Wiscott-Aldrich syndrome, acrodermatitis enteropathica, or Jacquet's dermatitis all cause characteristic diaper rashes. These are extremely uncommon, but should be considered in prolonged, severe rashes that are unresponsive to the appropriate therapy.

Skin wetness is the common denominator underlying the various causes of diaper rash. Even skin lesions of systemic illnesses tend to concentrate in areas where the skin is already damaged (the Koebner phenomenon). Urinary wetness increases skin friction, raises the skin pH, makes the skin less cohesive, and makes it more permeable, Ammonia from the urine. These effects combine to intensify the action of stool enzymes or other irritants that then inflame the skin"

What can I do to treat diaper rash?

Question: What can I do to treat diaper rash? And is there any way to prevent it in the first place?

A surefire way to cure diaper rash is prevention: Keep your baby's bottom dry and clean at all times. No doubt that's easier said than done! The following tricks help treat this common babyhood affliction:

• Change diapers frequently to reduce moisture on the skin.

• Air out the skin by leaving your baby's bottom bare whenever possible.

• Clean your baby's bottom thoroughly and pat it dry before putting a diaper on after a bowel movement.

• Avoid using irritants, such as diaper wipes and soap, to clean if it's only a wet diaper.

• Spread a thick layer of ointment — as recommended by your baby's doctor — to prevent urine from reaching the irritated skin.

• If all else fails, try a different brand of diapers or detergent if she wears cloth.