I am a healthy 51-year-old woman. For the last three years, I have been taking Eltroxin for an underactive thyroid. Even though I've been in the "normal" range for almost a year now, my hair still falls out - sometimes more, sometimes less. I now have very thin hair on top. My endocrinologist says it isn't due to my thyroid condition because of the normal results. My dermatologist says it's a side effect of the Eltroxin pills. Whom should I believe? Since I run and play tennis, could sweat from my scalp weaken the hair follicles, or perhaps certain minerals are lost due to sweat? Some people swear by products such as Roots HR or Royal Jelly, but others say it's all a big bluff. What is the truth? - L.B., Ramat Hasharon Veteran Jerusalem dermatologist Dr. Julian Schamroth answers: There are many causes of hair loss, but the most common are iron deficiency, thyroid disease, hereditary factors and a condition called telogen effluvium. Iron deficiency is due to insufficient iron consumption, poor absorption of iron or excessive loss of iron (such as blood loss from menstrual periods or after giving birth). A simple blood test will determine if you have an iron deficiency, and if so, treatment with iron tablets will usually resolve the associated hair loss within one to two months. Thyroid disease (an overactive or underactive thyroid) is a very common condition. It too is diagnosed by a simple blood test. Thyroid hormones can usually be controlled with oral drug therapy. Any hair loss associated with the thyroid condition should cease once the hormone levels are within the normal range. Hereditary factors are more difficult to treat. If there is a history of thin hair in this reader's mother or sisters, the hair loss is probably hereditary. There is a chemical called minoxidil (known commercially as Minoxi or Regaine) that can be rubbed into, or sprayed onto, the scalp. It is expensive, but it does improve hair growth. It has to be applied for at least six to nine months before it begins to take effect. Telogen effluvium is a specific form of hair loss that occurs three to six months after an incident of stress. The stress is very often pregnancy and delivery, but it may result from a surgical procedure, major illness or some physical or be psychological stress. There is no treatment for this condition, which resolves spontaneously. Other, less common, causes of hair loss can easily be excluded by visiting a dermatologist. Exercise and sweating does not result in mineral loss sufficient to cause any medical disease. Based on my patients' experience, I believe that shampoos, mineral and vitamin supplements, and the numerous over-the-counter preparations that claim to stimulate hair growth are a waste of time and money - and are very likely to disappoint users of these products. The other day my eight-months-pregnant wife choked a bit while eating. Luckily, no harm done, but it led me to wonder how would one safely perform the Heimlich maneuver on a pregnant woman? - B.D., Jerusalem Prof. Yoel Donchin, a senior anesthesiologist at Hadassah University Medical Center in Jerusalem's Ein Kerem and an expert in first aid, replies: The Heimlich maneuver for dislodging a foreign body in the trachea or the throat has been largely abandoned because of risks and general lack of effectiveness. But even when it was recommended, it never was permitted for use on pregnant women. Instead, a pregnant woman should try to remove it by coughing vigorously. Coughing produces very strong pressure and can push out the foreign body, but there are no solutions for everything. If the choking victim is turning blue, immediately call Magen David Adom at 101 for an ambulance and tell the person on duty that a person is choking on food or another foreign object. I do not recommend sticking fingers or other objects in to the person's mouth to pull out the object, as it could push it in farther. Open the victim's mouth and put her (or him) on the side, but never put pressure with your fingers on the chest or abdomen of a pregnant woman, She could get a tear in the spleen or the stomach or the fetus could be harmed. Rx for Readers welcomes queries from readers about medical problems. Experts will answer those we find most interesting. Write Rx for Readers, The Jerusalem Post, POB 81, Jerusalem 91000, fax your question to Judy Siegel-Itzkovich at (02) 538-9527, or e-mail it to email@example.com, giving your initials, age and residence.