My 17-year-old son in his last year of high school wears sandals or shoes and walks a lot. When he comes home, his feet really smell - whether he wears socks or not. What can be done? I am afraid he will be barred from entering class. - S.J., Tel Aviv Prof. Mel Rosenberg, Tel Aviv University microbiologist and the country's leading expert on odors and scents, replies: Foot odor is a common condition, caused by naturally occurring bacterial growth on the feet, especially when wearing socks and shoes. So I am sure your son is not the only one. But having really smelly feet can cause a great deal of embarrassment. In many cultures, it is impolite to remove your shoes in public, whereas in other cultures it is impolite not to remove them. Unpleasant foot odors usually emanate from moisture that comes from poor ventilation of the air - usually after the feet are inside footwear (shoes and socks) for a long time, especially when sweating. The human feet have more sweat glands than any other part of the body, and excessive perspiration of the feet occurs, especially in warm conditions. When the sweat doesn't evaporate, bacteria and fungi thrive on dead skin cells, resulting in smelly feet. The main kinds of bacteria that cause the foot malodor are Brevibacteria, Staphylococcus epidermidis and Propionibacteria brevibacteria. They reside on the soles of the foot and between the toes and convert methionine to methanethiol (which has a sulfuric aroma). These same bacteria produce the smell of certain kinds of cheese, which is why feet smells are often described as "cheesy." Staphylococcus epidermidis, which is also used in the production of cheese, produces isovaleric acid - another cause of smelly feet. The common vinegar-like smell of feet is probably caused by Propionibacteria and is due to the production of propionic acid by that type of bacteria. In some medical or physiological conditions, such as stress, hyperhidrosis (excessive sweating), hormonal changes and taking certain drugs, the prevalence of foot malodor may be greater, Here are some tips for preventing smelly feet: Wash your feet every day with warm water and soap (preferably an antibacterial soap). Dry the feet thoroughly with a dry and soft towel, especially between the toes. Air out your shoes regularly when you don't wear them. Use an effective shoe spray to reduce the smells and the accumulation of bacteria and fungi. Use foot powder to dry your feet and make sure you don't use excess powder (it may cause abrasion). Wear thick socks, so they can absorb the moisture and help ventilate the feet. Socks made of 100 percent cotton or wool are better for this purpose than synthetic socks (polyester or nylon) because they don't absorb sweat. Wearing nylon pantyhose or stockings may also cause excessive perspiration. Change socks at least once a day, or even more often if you sweat a lot. Wear shoes with adequate ventilation and refrain from wearing plastic or nylon shoes. Avoid wearing shoes without socks, as perspiration tends to increase in such situations. If this advice doesn't help, you'd better find a podiatrist. Some treatments such as those using electric-current devices can reduce perspiration for several weeks at a time. Other remedies for foot odor that your podiatrist may offer are alum, antiperspirants, paraffin bath treatments, ointments and other foot-care products. I am a 58-year-old man who underwent two operations on inguinal hernias (both sides) in the last five years. I was wondering whether there are any exercises I could do to strengthen the internal abdominal muscles and prevent a third operation, as hernias run in my family. - A.T., Tel Aviv Dr. Gal Dubnov-Raz, an expert in sports medicine at Sheba Medical Center, replies: Within a few months of hernia surgery, there is no reason why you should not exercise. After a hernia repair, the problem usually does not recur, but in some cases, it does. Strengthening the muscles of your trunk and abdomen is recommended, as this will improve your posture and reduce back pain. Exercises that move these parts of your body - called "the body core" - would be the best. Find a good trainer for tips on such exercises, which must be slow like Pilates. 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 firstname.lastname@example.org, giving your initials, age and residence.