Re: What causes birth marks

Birth marks are generally benign tumors (that is, growths that are not dangerous) that form on babies before birth or in the first few weeks after birth. Dermatologists (doctors who specialize in problems of the skin) refer to them as "nevi." The singular of "nevi" is "nevus" which, according to Hurwitz’ Clinical Pediatric Dermatology (2nd edition, 1993), is "a circumscribed congenital abnormality of any cell type present at birth." If that’s not confusing enough, doctors also call moles nevi, and they’re not technically birth marks at all, forming later in life.

Actually, no one really knows what causes birth marks. We know what they are and how they form and what to do about them. But why they start growing in some people and not others is a bit of a mystery. Sometimes they seem to run in families, so genetics may (or may not) play a role, but mostly, they just happen. It will take future Mad Scientists like you to find out what triggers them off.

Let me tell you about some of the most common nevi:

Strawberry hemangiomas are lumpy, red areas made up of clusters of blood-vessel-like tissue with capillaries poking out which make them look and feel like strawberries. These are usually on the baby’s head, neck, or trunk and will usually go away on their own if you leave them alone.

Salmon Patches are flat, dull pink patches that occur in 30 to 40 percent of newborns. They usually show up on the eyelids, above the nose, or on the back of the neck. People call the ones on the back of the neck "stork beak marks" because it’s a fun thing to say. These marks are also blood -vessel related and need not be treated since they generally fade away with time.

Port-wine stains are made up of dilated capillary-like vessels. They are purple-red in color, usually flat or slightly raised, and do not disappear with time. Again, since they don’t cause any trouble, you can leave them alone. Some people don’t like how they look so cover them with makeup. Zapping them with short bursts from a pulsed tunable dye laser can treat about 94 percent of port-wine stains without scarring.

Pigmented nevi appear within the first three days of life in 4 percent of infants. These may have brown-to-black irregular surfaces, sometimes with hair growing on them. Most of these are pretty small, but some can be really big -- like covering a whole arm or leg, or a whole back. The big ones are sometimes associated with other medical problems and are monitored carefully by us pediatricians.

Café-au-Lait spots (French for "coffee with milk") are light-brown irregular spots with an unraised border. Ten to twenty percent of people have them, again without any problems. People who have a bunch of fairly large ones may have associated medical problems that need to be investigated.