Q. What causes hair to change its color and texture with age? Also why do age spots develop on the skin? can these changes be prevented?

A. Age-related changes in hair and skin are largely under genetic control. For the most paet, these changes can't be prevented. That leaves two other options for combating these developments: slowing their progress or disguising their appearance.

Hair becomes thinner, grayer and, in some people, curlier with age. Hair dyes and colorings are about all you can do to turn gray to another color.

Aging skin also becomes thinner and in some people develops light brown spots or blotches known as age spots or liver spots. These areas contain more of the skin pigment melanin and have nothing to do with your liver at all, except that they resemble it in color. Age spots occur more frequently on sun-exposed areas -- the face, hands and forearms.

Sunlight speeds the aging of the skin and can lead to sun-induced skin damage and skin cancer. Sunlight also helps bring about new age spots and causes existing ones to grow darker, so using a sun-block skin cream may help retard their development. In any case, sun screens are good for preventing skin damage from the sun, especially in light-skinned people.

Skin lighteners, available by prescription, will temporarily decrease the amount of pigment in age spots. These work best when used with sun blocks. Skin lighteners, which may be irritating to some people, don't permanently cure age spots. Over-the-counter products are less concentrated and less effective than the prescription medicines.

A dermatologist can also briefly freeze the spots with liquid nitrogen, which will make them fade. This is the most effective treatment for troublesome age spots.

Q. You recently wrote about the new nicotine chewing gum. Is there a good reason that it's available by prescription only? I think I could get my husband to try it if I bought him a supply, but I will never get him to go to the doctor for a prescription.

A. Nicotine chewing gum should be used only with professional supervision for two main reasons:

* Nicotine can worsen some medical conditions, such as coronary artery disease (hardening of the heart's arteries).

* About 5 percent of users seem to become addicted to the gum.

The gum seems to work best when part of a smoking cessation program; a casual trial of the gum is probably much less effective.

If all other measures fail with your husband, you might ask your family doctor for some help in getting your husband into the office. But unless the motivation to stop smoking comes from your husband, I'm doubtful about his chances for success.

Q. Our 14-month-old daughter often has hard bowel movements. Is this normal? If not, what can we do to correct it?

A. The number of bowel movements normal babies have each day varies widely, depending on the baby, the diet and age. On the average, infants have two to five bowel movements a day and children older than 18 months have one to three. But normal babies may have a bowel movement as seldom as every two to three days or as often as six or more times daily. So compare your baby's frequency with her customary pattern rather than another child's to decide when she's irregular.

Stool consistency also varies, depending on the individual baby and dietary factors. Breast-fed babies tend to have softer and more frequent bowel movements. Many babies grunt, strain and turn red in the face when having a normal bowel movement. Parents often mistake these normal actions as signs of constipation.

The most reliable sign of true constipation in a baby is the presence of hard, ball-like stools. Lack of adequate water and fiber in the diet is the most common cause. Increasing the amount of water, fruits and vegetables and whole wheat cereals in your child's diet should help. Prune juice or carrots are other dietary aids for constipation. A temporary home remedy is adding a tablespoon of Karo corn syrup to four ounces of water. The sugar acts as a mild laxative, but I don't recommend doing this regularly because of the risk of dental cavities.

Rarely, severe constipation in a baby is a sign of an intestinal problem called Hirschsprung's disease, so check with your baby's doctor if the constipation is persistent.