DEAR DR. DONOHUE: Many years ago, when I was still a teen, I went skiing with my older brother. He was a much better skier than I, so we went our separate ways. Later, on the way to get something to eat, I saw a group huddling around one skier who looked a lot like my brother. It was my brother. He lost one of his gloves, and he had two frostbitten fingers. His only permanent damage was the loss of a fingertip. Ever since, I have been careful about dressing warm, often with two pair of gloves in cold weather. I don’t know what to do about frostbite. Will you run the basics by me? — S.S.

ANSWER: Frostbite happens when the temperature drops to 32 F (0 degrees C) or lower. Actually, the temperature has to be lower than 32, since the minerals in the fluids bathing the tissues lower their freezing point.

The places most susceptible are the fingers, hands, toes, feet, nose and ears. The first sign of trouble is pain. Then the skin turns quite pale. After that, numbness sets in. People might think that nothing is wrong at this stage, but numbness is a sign that freezing is imminent. The skin and involved tissues become hard and firm.

Ice crystals form in the spaces between cells. They pull water out of the cells and dehydrate them. The dehydration, decreased blood flow and ice crystals all work together to cause tissue damage. One of the most destructive factors is the lack of oxygen that comes from artery constriction to prevent heat loss from the rest of the body.

Fast rewarming is the treatment. It should not begin if you are in a place where there’s a chance of refreezing. Refreezing is a more destructive process than leaving things alone until you are in a place where the person can be kept warm.

The affected part should be immersed in a bath of hot water whose temperature is around 104 F (40 C). The water has to be kept warm by adding more hot water as the bath begins to cool. At no point should you rub the frozen part. If the affected area cannot be warmed in a water bath, then use hot compresses.

Rewarming is painful. Tylenol or a stronger medicine should be given. In 12 to 24 hours, blisters form. Do not break them. At this point, have a doctor examine the patient for definitive care.

DEAR DR. DONOHUE: Does it hurt you to exercise if you have a cold? I do it all the time, and I can’t see that it makes anything worse. I’ve been told not to do so. — B.R.

ANSWER: If you’re coughing, sneezing or have a dripping nose, others are not going to appreciate exercising along with you.

A general rule says if your symptoms are above the neck, it’s OK to exercise. Such symptoms would be a stuffy or runny nose, a scratchy throat and an occasional sneeze.

If you have an elevated temperature, achy muscles or a persistent cough, don’t exercise.

DEAR DR. DONOHUE: While playing basketball, I got tripped and landed on my left arm and shoulder. It felt like lightning had struck my arm. My arm and hand were numb for a short time. Within a few minutes everything was back to normal. I could move my arm and shoulder without pain. My mom thinks I should have stopped playing and wants me to see a doctor. Is this necessary? — C.P.

ANSWER: You’re describing what sounds like a burner, a common football injury. Nerves in the chest near the shoulder have been stretched. That brings on a burning sensation in the arm and hand. The sensation is short-lived.

It’s fine to return to play if a person can move the shoulder, arm and hands in all directions and if pain is completely gone.

You don’t need to see a doctor now unless you have some symptoms.

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.