DEAR DR. DONOHUE: I have a basal-cell skin cancer and am scheduled to have Mohs surgery for it. What causes it? How is this surgery done? How long will I be laid up? Is this a life-threatening cancer? – R.S.

ANSWER: Basal-cell skin cancers constitute 80 percent of all skin cancers, not including the most serious skin cancer – melanoma.

The cause is believed to be intense, intermittent exposures to sun during childhood and young adulthood – the kind of exposures that bring on sunburns. Close to 80 percent of basal-cell cancers occur on skin subject to sun exposure – the head, face, ears, neck, arms and legs. A few basal-cells arise on skin that rarely sees the light of day, so sunlight is not the sole cause.

It begins as a pearly nodule, about the size of a small pebble, whose surface is often covered by a cobweb of tiny blood vessels. The nodule forms an ulcer that might bleed or scab. It often heals, but the sore returns. Any recurrent skin sore should bring a person to the doctor.

Basal-cell cancers are just about always curable. They don’t threaten life. If not treated, however, they can bore deeply into tissues and cause local destruction.

Mohs surgery is the procedure where the doctor removes thin slices of the basal-cell, examines the slices with a microscope, and keeps removing more slices until he or she reaches a level when no more cancer is seen. It has an excellent cure record. It doesn’t lay people up at all.

Other ways of treating basal-cell cancer depend on its size and its location. These cancers can be scraped off with a special instrument, dried with electric current, frozen or treated daily for six weeks with Aldara cream. Your treatment is an excellent one.

DEAR DR. DONOHUE: I have obstructive sleep apnea and also have GERD. Both are under control with treatment. Is there any exercise to keep my airways from collapsing and blocking airflow? How about exercises to improve my sphincter muscle? – H.D.

ANSWER: Sleep apnea comes from redundant tissue in the back of the mouth and throat that constricts the opening through which air passes into the lungs. Weight reduction, if called for, sometimes opens up the constriction, but there is no exercise that will fix it.

A sphincter (SFINK-tur) is a muscle that wraps around body passageways. When a sphincter contracts, it closes the passage. When it relaxes, it opens the passage.

The esophagus is a muscular tube running from the throat to the stomach. Through it, swallowed food reaches the stomach. At its lowermost level, a sphincter keeps it closed to protect it from the upsplashing of stomach acid. If the sphincter muscle is weak, stomach acid can get into the esophagus to bring on heartburn – GERD, or gastroesophageal reflux disease.

There is no exercise that strengthens the esophagus’ sphincter. There are many medicines that slow or stop the production of stomach acid or neutralize its effects.

The booklet on hiatal hernia, heartburn and acid reflux digs much deeper into this topic, its causes and treatments. Readers can order a copy by writing: Dr. Donohue – No. 501, P.O. Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6.75 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: Eleven years ago, I had a chest MRI. The chest reading was OK, but they saw a hemangioma on my liver. I have had ultrasounds since, and there are two more liver hemangiomas. Do these ever turn into cancer? – L.B.

ANSWER: Liver hemangiomas are small balls of tangled blood vessels. They aren’t cancer and don’t become cancer. Nothing is done about them unless they grow so large that they disrupt liver function. That seldom happens.

DEAR DR. DONOHUE: My son, age 43, has neurofibromatosis. Doctors tell him there is no cure. I read that injections of hydrogen peroxide remove the tumors. Is this correct? – J.S.

ANSWER: Neurofibromatosis is an inherited condition where nerves sprout rubbery, noncancerous growths mostly on the skin. The growths are neurofibromas, and they can number from a few to thousands. If neither parent has the neurofibroma gene, then a mutation occurred in the patient’s gene pool.

Neurofibromas are not cancer, but in rare instances one might become cancer. Skin neurofibromas can be a cosmetic problem, and neurofibromas that develop next to the spinal column can compress nerves and cause trouble, but most neurofibromas are not a threat to health.

These growths are usually not present in infancy or young life. However, if an infant has six or more tan skin spots 0.8 inch in diameter or larger, that is a tip-off that the child has the illness. Those spots are called café au lait spots – French for coffee with cream, the color of the spots. The neurofibromas appear as the child ages.

Doctors taking care of these patients have to look for signs of brain tumors, for the illness imparts a propensity toward such tumors.

There is a less-common variety of this condition in which the hearing nerves are affected.

There is no cure. Hydrogen peroxide injections are not recommended treatment.

You and your son would do well to contact the Children’s Tumor Foundation, formerly known as The Neurofibromatosis Foundation. The name change was prompted by the public’s lack of familiarity with the word “neurofibromatosis.” The foundation’s toll-free number is 1-800-323-7938, and its Web site is www.ctf.org.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.