DEAR DR. DONOHUE: My dad is 84 and in good health except for diabetes, which he controls with pills and diet. He has a spreading red rash on his left leg, just above the ankle. I took him to a doctor, and the doctor told us it was cellulitis. He has my dad on antibiotics. The doctor said if things don’t turn around within two days, he will have to hospitalize my dad.

What is cellulitis, and how dangerous is it? — W.C.

A: Cellulitis is an infection of skin cells (hence “cellulitis”) and the tissues and fat beneath the skin. It can happen at any age, but more often it’s encountered in older people. People who have had a leg vein removed for cardiac bypass surgery and people who have had lymph nodes taken during cancer surgery are more susceptible to it. Your dad’s diabetes makes him vulnerable to all infections, including cellulitis.

Staph or Strep germs are responsible for most cases. These germs gain access into the skin through a scratch or cut, either of which can be so small that it goes unnoticed. Athlete’s foot provides another opportunity for bacterial invasion of the skin.

Infected skin turns red, hot and becomes swollen. It is quite painful. Spread is rapid. A person can almost watch the red margin advancing.

Cellulitis can be a dangerous infection if it goes untreated. A slowly progressing infection confined to a limited area can be treated at home with antibiotics. An infection that’s advancing quickly requires intravenous antibiotics in the hospital.

Most people weather a bout of cellulitis without any significant consequences except a terrible memory of the experience.

DEAR DR. DONOHUE: I have a bunch of brown, soft patches on my back and upper arms. They look a little like flat cauliflower. What are they? They don’t hurt or itch, but they look disgusting. Can they be removed? — D.R.

A: You must realize that a diagnosis by letter is, at best, a wild guess. I believe you’re talking about seborrheic keratoses. They aren’t cancer, and they don’t become cancer. They appear mostly in people over 50. Their diameter varies from small to greater than an inch. It looks like someone has pasted them on the skin. Their surface is rough and fissured — in a word, warty. Most often, they’re uniformly brown and rarely cause any symptoms.

It’s not safe to the play odds when it comes to brown or dark-colored skin patches. You need a professional eye to determine the exact nature of such things. You don’t describe a melanoma, the most serious kind of skin cancer, but you don’t want to take any chances by guessing.

Seborrheic keratoses can be removed easily. They can be frozen off; they can be scraped off; and sometimes they succumb to the application of cortisone ointments or creams.

DEAR DR. DONOHUE: My mother and her two sisters gained a tremendous amount of weight after menopause. I am nearing that age, and I dread the same fate. Is this a genetic trait, and am I doomed to the same thing? — N.D.

A: Many women gain 5 to 10 pounds after menopause unless they are extremely careful in watching their calorie intake and unless they faithfully exercise.

Why this happens isn’t clear. It seems that everything that happens to a woman after menopause is explained by the diminished production of estrogen, but there’s no proof that weight gain can be linked to a dropoff in estrogen. It probably has more to do with a cutback in physical activity.

Most everything has roots in genetics, but this is a trait that can be altered by exercise and diet.