DEAR DR. DONOHUE: Are eggs harmful? I’ve been told not to eat more than two a week. I read, however, that eggs are good for us. – M.D.

ANSWER: The daily cholesterol limit has been set at 300 mg. An egg has 212 mg of cholesterol, so a single egg just about polishes off the entire day’s cholesterol allotment.

However, the 300 mg limit was set in a time when it was believed that most blood cholesterol comes from foods high in cholesterol. That isn’t true. Most blood cholesterol comes from our liver’s production of it. Saturated fat and trans fat, not cholesterol, prod the liver into making cholesterol. Diet restrictions to lower cholesterol, therefore, should focus on those fats and not so much on cholesterol. Unless your doctor has you on a very stringent cholesterol-lowering diet, the rule on egg limitation can be relaxed.

A little while ago, a study compared those who ate one or two eggs a day with those who ate fewer than one a week. The egg-eaters were not more likely to die from heart disease than were the abstainers. The only exception was people with diabetes. Diabetics who ate eggs daily were a little bit more at risk of dying from heart disease than were the ones who seldom ate them.

Eggs are a nutritional bargain. One egg has 6 grams of protein and many of the B vitamins. It also has vitamins A and D. Lutein and zeaxanthin are found in eggs. They are important for eye health. All of this, and eggs are cheap.

One egg a day is permissible for most people. If a person wants to eat two, that’s OK. Just skip the next day’s egg.

DEAR DR. DONOHUE: I was told by a friend that there is only one way a man can get a urinary tract infection, and that is by having intercourse with a woman who has an infection. I would like to know how a man gets a urinary tract infection.

Three years ago, my husband was in considerable pain, and we went to the emergency room. My husband had a urinary tract infection, and the doctor said he probably got it from me. I did not have an infection at that time. Later I asked my husband if he was having an affair, and he swore he wasn’t.

Last month he came down with another urinary tract infection. Is he cheating on me? – Anon.

ANSWER: Urinary tract infections are not sexually transmitted diseases. No one should think they are.

Women have more urinary infections than men because the female urethra – the tube draining the bladder to the outside world – is shorter than the male urethra, and bacteria can ascend it to reach the woman’s bladder quite easily.

Men can also get a urinary tract infection through the ascent of bacteria in their urethras. It doesn’t happen as often as it does with women.

The urinary tract in men can be infected by bacteria traveling in the blood from a distant infectious site and settling there.

Men can also get urinary tract infections from infected structures adjacent to the urinary tract. Prostate infections are an example. Germs infecting the prostate can gain access easily to the urinary tract.

There are some sexually transmitted diseases that infect the urethras of both men and women. Gonorrhea and trichomonas are two such infections. Those are sexually transmitted diseases, not urinary tract infections.

The urethra of the male is both a urinary tract passage and a passage for sperm. It’s part of his genital tract as well as his urinary tract.

DEAR DR. DONOHUE: My hair is falling out. I just run my fingers through it, and hair comes out. I have had Addison’s disease, two brain tumors and polycystic ovary disease. Please help me save my hair. I am 43. – N.W.

ANSWER: You have a complicated medical history. Some of your past illnesses could contribute to hair loss. Hair loss in Addison’s disease is common. (Addison’s disease is a shutdown in the production of adrenal-gland hormones.) Replacing the lost hormones ought to stop hair from falling out. Polycystic ovary disease can also lead to hair thinning. Your doctors have to take care of those problems for you.

Some hair facts can give you an idea of what is normal and what isn’t when it comes to shedding hair. There are more than 100,000 hairs on the head. It’s normal to lose 100 to 150 hairs a day. For the next week, count the number of hairs in your brush and comb, and on your pillow and clothes. If there are more than 150 each day, your hair loss is excessive.

Autoimmune disorders like lupus, iron deficiency, physical and mental stress, some medications, too much or too little thyroid hormone, excess male hormone and a low-protein diet are just a few of the causes of thinning hair. A doctor has to look for those causes and prescribe treatment based on which cause is discovered.

If no cause can be found, then there is Rogaine. Rogaine treatment, however, requires lifelong commitment. When a person stops using it, hair begins to fall out again. If you’re making too much male hormone, birth-control pills can counter the effects of male hormone on hair loss. So can the water pill Aldactone.

You cannot make any progress until hair-loss causes are investigated.

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