DEAR DR. DONOHUE: When my son was a teen (he’s 35 now), he lost the tip of his index finger because it was frostbitten while he was on a camping trip. He was a saxophone player, and it affected his ability to play. What can you say about frostbite and its prevention? I know a lot of people who are ignorant about it. Can people become acclimatized to cold, as they do to heat? – R.P.

ANSWER: Acclimatization to cold is modest at best. It takes longer to get used to cold than it does heat, and the changes that occur are not great. One change that takes place upon repeated cold exposure is lessening of shivering. Experts aren’t sure if this is good or bad. Shivering comes from muscle contractions, and those contractions generate body heat. It is true, however, that there is a slight enhancement in conservation of body heat after repeated exposure to cold.

Frostbite can happen to anyone, even those who, year after year, spend long hours in the cold. Prevention entails keeping dry, wearing appropriate clothes and recognizing the signs of imminent trouble. Water conducts cold faster and to a greater degree than air, so dryness is of utmost importance. Cold-weather dressing should be done in layers. When exercising in the cold, outer layers can be shed to prevent excessive sweating. The hands, feet, nose, cheeks and ears are the places most likely to suffer from frostbite. Mittens keep the hands warmer than gloves, but they impede dexterity. If gloves are to be used, they should be lined. Don’t blow into the gloves. That provides moisture that’s apt to freeze. Don’t coat the hands or feet with petroleum jelly. The nose, ears and entire face should be protected if a protracted amount of time is spend in the cold.

The first sign of trouble is numbness. It should alert people to get inside. Shortly after, the skin might redden and then turn waxy-white. Definitely get inside if these changes occur. Blisters signal real trouble. Ice crystals form in the skin and in the tissues below the skin. They cause damage, but the greatest damage occurs from a decrease in blood supply due to intense artery constriction. If freezing occurs, rewarm rapidly by immersing the affected part in water whose temperature is 99 to 102 F (37 to 39 C) for 15 to 30 minutes. It’s best to let an expert take charge of this treatment. In other words, get to the emergency department of a hospital.

DEAR DR. DONOHUE: I am 14 and run cross country. I have ankle and knee pains and digestive problems. If I run a race, I get diarrhea, and sometimes it lasts a week. I am losing a lot of weight. I don’t know how to cure this. – M.F.

ANSWER: Distance running causes many people to have diarrhea. From 19 percent to 26 percent of marathoners develop it during a race.

Apparently the diversion of blood from the digestive tract to the leg muscles is so great that the tract cannot process food and food residue, so diarrhea results.

Eat at least three hours before a run. The meal should be low in fat and fiber. Don’t eat or drink any dairy products before running, and don’t use any artificial sweeteners. Don’t drink pop. Stay hydrated with sports drinks.

Decrease the length of your runs and your speed. Gradually work back to your current mileage and speed.

If none of this solves the problem, you have to see the family doctor. Something more serious might be going on. You can’t afford to lose weight, at your age. The doctor also can examine your ankles and knees.

DEAR DR. DONOHUE: I read about walking with 2-pound hand weights. What do you think of this? – K.B.

ANSWER: The weights increase the calorie burning of the walk and are OK if they don’t make your elbows, shoulders or neck hurt. Start with 1-pound weights. Swing your arms as you usually do, but don’t exaggerate the swing. Don’t use weights heavier than 3 pounds.

DEAR DR. DONOHUE: What do the initials ALS stand for in the illness also known as Lou Gehrig’s disease? How does it affect the human body? Is there any merit in identifying toxins in the body by sampling a person’s hair and detoxifying that person for a possible cure? – Anon.

ANSWER: “ALS” stands for “amyotrophic (AY-my-uh-TROWE-fik) lateral sclerosis.” “Amyotrophic” means “muscle wasting.” “Sclerosis” means “scarring.” The scarring takes place in the brain and spinal cord, and it destroys nerves that control muscle movement. That leads to muscle wasting and eventual loss of all movement. The patient becomes a prisoner in his or her own body. The famous baseball player Lou Gehrig had this illness.

I know of no hair test that reveals toxins that lead to ALS or of any toxin that can be removed from patients for a cure.

If you want to read a touching story about a man with ALS, pick up a copy of “Tuesdays With Morrie” by Mitch Albom.

DEAR DR. DONOHUE: I take a fish-oil supplement daily. Can you tell me if these tablets contain mercury, as some fish do? – P.C.

ANSWER: Take your fish-oil supplement without fear. Such supplements contain negligible, if any, amounts of mercury. They won’t make you sick. They could make you well.

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.