La Jolla, Calif.: I teach surfing every summer and have visitors from Europe. Their sunscreen, although labeled in a similar way (with SPF numbers), seems to work better. I've heard there are ingredients not approved by the Food and Drug Administration that are used in European sunscreens. What are the ingredients and why aren't they used in America?

The methods used to determine a product's SPF (or sun protection factor) in the United States and Europe are different. The U.S. method is less exact and often overstates true protection. Sometime this year, the FDA is due to propose new rules which will make our SPF numbering system more reliable and probably will limit the maximum claimed SPF to 30. Currently, there is little difference in the effectiveness of U.S. sunscreens labeled SPF 30 versus SPF 45. Most nonopaque sunscreens available here effectively block UVB, the shortwave part of the ultraviolet spectrum that causes sunburn, but are not very effective in blocking longer wavelengths. You've probably heard about Mexoryl (drometrizole trisiloxane), a chemical that blocks longer-wave ultraviolet (UVA), which probably plays a role in skin aging and pigmentation. While Mexoryl is not much better at protecting against sunburn than high-SPF sunscreens available here, its advantage over other effective UVA-blocking products available in the United States (such as titanium dioxide), which are opaque, is that Mexoryl is clear. L'Oreal, the manufacturer of Mexoryl, has undertaken an extensive campaign aimed at obtaining approval from the FDA for use of Mexoryl in the U.S. As of May 2006, the FDA, whose regulations forbid making public its concerns, had not yet ruled on the matter.

Dalton, Ohio: My 23-year-old son has had a fungal infection of the hands and feet for at least three years. Topical antifungals, and now two months of oral antifungal medication, haven't helped. What next?

Fungal infections affecting both hands and both feet that do not respond to topical and oral antifungals over long periods of time are infrequent in people with normal immunity and without unusual exposures to warm and moist environments. Such a persistent and treatment-resistant condition requires a thorough assessment which might include skin biopsies, cultures and a complete dermatologic examination--not only of hands and feet but of all body surface areas. Also, if your son's health history indicates any concern, his immunology status should be evaluated. Finally, an investigation of family health histories may reveal possibly related problems. Psoriasis, eczema, contact dermatitis and some genetically determined conditions, which may not appear until adolescence or adulthood, can easily be mistaken for fungal infection and may require different treatments. Consulting a dermatologist may help in getting to the root of your son's problem.

St. Louis, Mo.: I recently had heart-valve-replacement surgery. I would like to heal my scar in the best way possible. Can you recommend products or procedures?

The extent of scarring at a surgical site largely depends on six factors: 1) the depth and size of the injury or excision, 2) how it is repaired, 3) its location, 4) movement or stretching during healing, 5) avoiding infection of the site, and, most important, 6) the individual's genetic tendency to scar. Unfortunately, the site of heart surgery is very prone to developing scars. Once sutures have been removed, moisturizers and perhaps massage may help reduce scarring. A variety of agents, including Mederma and vitamin E, have been promoted as helpful in reducing scars, but available studies indicate that they provide no additional benefit beyond moisturization. Remember that many scars improve on their own with time. Therefore, unless the scar is painful, itchy or thick, I do not generally recommend treatment for about a year. For itchy or thick scars, intralesional steroids are simple, safe and often helpful. For very troublesome scars that do not respond to intralesional steroids, scar revision surgery and lasers can sometimes bring improvement.

Dallas, Texas: Is it safe for a pregnant woman to get a chemical peel or microdermabrasion? Are there other skin-care products that I should avoid?

A good rule is to avoid all medically nonnecessary procedures and treatments during pregnancy. However, because microdermabrasion is only a mechanical process, it should be completely safe during pregnancy, except for the very minor stress associated with the procedure. How safe a chemical peel is depends on the agent being used in the peel. For example, deep peels with phenol should absolutely be avoided; but a superficial peel with alpha hydroxy acids is very unlikely to be a problem. Tretinoin, the active ingredient in Retin-A and Renova, and other retinoids should also be avoided during pregnancy. Unfortunately we know very little about the safety of topical over-the-counter products during pregnancy. Most are probably safe. Still, it is prudent to use only what is needed during pregnancy, which for most people is soap, moisturizers and sunscreen, particularly those that contain physical blocks such as titanium dioxides.

Seattle, Wash.: When I go out in the sun, even when I wear sunscreen, I get brown blotches all over my forehead, cheeks and upper lip. My dermatologist says the only thing that can be done is to wear sunblock and a hat whenever I'm outside. Is there anything else I can do?

The problem you describe is most likely a condition called melasma. For reasons not now understood, the melanocytes (pigment-producing cells) in the areas you describe have been changed in a way that causes them to produce more melanin than the same cells in surrounding areas. Sunlight exposure increases the contrast between affected and surrounding skin. Although melasma can occur in anyone, most people affected by it are women who are using or have used oral contraceptives or are or have been pregnant. The condition may first appear while using oral contraceptives, during pregnancy, or up to a year or more afterward. Unfortunately, once melasma has occurred, it may recur at any time and often persists long after a person has stopped birth-control pills or is no longer pregnant. Melasma can be treated with a variety of topical therapies including retinoids, such as Tretinoin (Retin-A), and "bleaching agents" that contain hydroquinone. Chemical peels and laser have also been tried with varying results. Success rates for all treatments are modest. Unfortunately, even if the pigmentation is lightened, unprotected sunlight exposure often causes it to reappear. Therefore, very vigorous sun protection using agents that block UVB and UVA, such as the products you describe, is essential.

Stern is chairman of the Department of Dermatology at the Beth Israel Deaconess Medical Center and the Carl J. Herzog professor of dermatology at Harvard Medical School. He joined the staffs at both institutions in 1976. In addition to patient care and teaching of residents and students at the Beth Israel Deaconess Medical Center and Harvard Medical School, his research has focused on the prevention and treatment of skin diseases including skin cancer, photoaging, psoriasis and acne. He has served as coeditor of two dermatology journals and on the editorial board of other journals and he recently completed a service as chairman of the USFDA Dermatologic Drug Advisory Committee. For more information, go to www.health.harvard.edu Readers should consult a medical professional for an accurate diagnosis.