One retired secretary in Gaithersburg wears turtleneck sweaters and long sleeves to hide it. Another woman will not undress in front of her husband because of it, and a college professor who teaches in Maryland uses makeup to cover it.

'It' is vitiligo, a little understood disease that causes the skin to turn completely white. The condition is often mistaken for burn scars and is thought by many to be a disease peculiar to blacks, only because the drastic difference in skin color is much more noticeable on blacks. In fact, vitiligo affects 2 to 4 percent of the U.S. population and is indiscriminate of age, sex or race.

Though the disease doesn't seem to affect the general health and is not contagious, it is embarrassing for some people and thus can be a real source of emotional anguish.

"They see themselves as hideous monsters; some are recluses," says Dr. Pearl E. Grimes, who runs the Tuesday/Thursday vitiligo clinic at Howard University Hospital in the District.

The clinic is part of a four-year, $2 million Natinal Institutes of Health grant to six facilities. The others are Yale University, University of Pennsylvania, Bryn Mawr College, University of Massachusetts and Massachusetts Eye and Ear Infirmary.

These centers are investigating the causes of vitiligo, its psychological impact, methods of treatment and its possible relationship to any other physical conditions.

Howard is the only specialized treatment facility in this area of the country. Not many people know about the clinic, however, because few dermatologists are familiar with the disease and therefore are not willing to handle vitiligo patients. Grimes and her team have treated 180 patients since the clinic opened in January 1980.

While vitiligo, especially on the hands or face, can be traumatic for black patients, it can be equally devastating to some whites, "especially darker-skinned Caucasians and those who tan," says Grimes.

A 55-year-old college professor, who is Chinese, said he only recently gave up the messy makeup he used to cover the ghostly white patches on his right hand -- the hand he uses to write on the blackboard. "Now my students know."

"I made up my mind to fight this psychological problem," said the professor, who did not want to give his name. But he says he's still not anxious to shake hands and is uneasy when strangers notice the condition. He is quick to add, though, that "I am fascinated by the cellular process."

"I think this place is doing me a lot of good," he says of the Howard clinic, but he worries that the vitiligo will spread to other parts of his body.

A treatment for the condition, once confused with leprosy, was discovered by anicent Egyptians. The Egyptians ate psoralen berries, then sunned themselves on the banks of the Nile to regain their natural color. Psoralen lotion and pills are still used in conjunction with ultraviolet light, and the treatment is significantly effective in about 40 percent of cases, Grimes said.

"If they are conscientious about taking their medications, they'll get some response," says Grimes, but she adds, "We have no panacea," and treatment is a time-consuming process. The clinic enrollment fee is $35, and subsequent visits, usually once every week or two, cost $10.

White vitiligo, the pigment cells, called melanocytes, are destroyed and usually are not replaced. Psoralen promotes the growth of new melanocytes, and with the help of real or artificial sunlight, these new cells migrate to the areas that have lost pigmentation.

According to researchers in Connecticut and Massachusetts, in some individuals vitiligo seems losely related to other autoimmune diseases -- those in which one system of the body works against another. Diabetes, thyroid irregularities and loss of eye color are seen in some vitiligo patients. In some instances, the skin disease appears to be inherited.

According to Grimes, another common denominator in many patients is the appearance of vitiligo shortly after a stressful event. The professor isn't surprised at this. He noticed the first white patch on his thumb in 1971, just after he completed his thesis.

"It got worse when I got struck with some sort of allergy," says a nervous Olga Schmid. "It's not a beautiful sight." She has had vitiligo for 10 years and says it is "progressing very rapidly" over most of her body, despite treatment with psoralen pills and ultraviolet light.

Another Maryland woman, who developed the disease on her hands, chest and back following breast surgery nine years ago, says, "I think it bothers other people more than it bothers me." But when a friend introduced her to his mother who also had vitiligo, the woman recalls, "It really made me feel better to talk to someone about it."

She has been reluctant to seek treatment because few physicians have been able to tell her much about the disease. Recently, a co-worker whose son has vitiligo told her about the Howard clinic. "Perhaps one day I'll seek treatment," she says hesitantly.