I have a dark coating, almost black, on my tongue. The surface of my tongue seems to be rough in appearance, almost wrinkled. What could it be?

D.P.

Two possibilities come to mind: "black hairy tongue" and "fissured tongue" (which proves that not all medical terms are incomprehensible).

There's just one bit of anatomy that you need to know. The upper surface of the tongue is covered by the taste buds (medical term: "filiform papillae"). Viewed microscopically, the papillae look like a forest.

Individuals with "black hairy tongue" merely have a taller-than-normal forest of papillae. The extra height comes from an accumulation of keratin, which is the chief protein found in hair and skin. Normally, keratin sloughs continuously and gradually from mucous membranes and skin. (In fact, "discarded" skin cells are the chief constituent of house dust. There is a critter that makes its living by eating this stuff: the dust mite. People who are "allergic to dust" are usually just allergic to dust-mite poop!) In people with black hairy tongue, not enough keratin is sloughed (or, perhaps, too much keratin is being produced at the surface of the tongue).

No one knows for certain what causes black hairy tongue, but there are several well-known associations. ("Association" means, "We see A and B occurring together, but we're not sure whether A causes B.") Black hairy tongue is fairly common among smokers. It is also sometimes seen following treatment with antibiotics. Other associations with black hairy tongue include radiation therapy to the mouth, poor oral hygiene, frequent use of strong mouthwashes and frequent use of antacids.

In most cases, black hairy tongue is more of a cosmetic problem than a functional problem. Nevertheless, some folks with black hairy tongue also have bad breath and/or a bad taste in the mouth. The usual recommended treatment: Eliminate possible causal factors, and scrape (or brush with a toothbrush) your tongue on a regular basis.

You also used the phrase "almost wrinkled" to describe your tongue. This brings to mind a separate condition, "fissured tongue" (also known as -- and I'm not kidding -- "scrotal tongue"). In this condition, there is no discoloration, but there are numerous fissures (cracks) on the upper surface of the tongue. This condition is usually asymptomatic, although some people with this problem also have problems with burning tongue. No treatment is necessary.

Bear in mind, of course, that I have not seen your tongue, so I cannot be certain you have either of these problems. Most primary-care providers are familiar with these conditions, so I suggest you show your tongue to your family physician; if the family doc is stumped, an oral surgeon or ear, nose and throat doctor (ENT) could certainly figure this one out.