Cosmetic claims are not regulated by the FDA — products can claim to “firm” or “repair” skin or to make you look “younger” and these benefits needn’t be proven. Only a few substances have a demonstrated ability to reduce or prevent wrinkles, and even those effects are modest.

Moisturizers: The basics

No moisturizer can make wrinkles disappear or prevent new ones from forming, and none can stop the effects of gravity or exposure to sunlight. However, moisturizers can soothe dry skin and temporarily make wrinkles less noticeable.

Petroleum jelly is probably the most effective and least expensive moisturizer because it coats the skin and seals in moisture. But it looks and feels greasy. Creams (which generally contain more oil than water) and lotions (which contain more water than creams) are a better choice. Many moisturizers are humectants, an oil-free class of moisturizer that reduces the loss of water by binding it to the skin. This helps prolong the product’s softening effects. Two other common ingredients, propylene glycol and sorbitol, both bind moisture to the skin and repel it, canceling out any benefit. The American Academy of Dermatology suggests avoiding them. Some skin creams contain botanical ingredients, such as jojoba oil, coconut oil, safflower oil, and linoleic acid, which help maintain the skin’s outer protective layer and the natural oils that keep the skin supple.

Vitamins and antioxidants

There’s no proof that vitamins or antioxidants applied directly to the skin do much at all. Nor is it known whether they remain active long enough to prevent cell damage, promote new collagen production, or confer other benefits. Vitamin C (ascorbic acid), for example, quickly loses potency when exposed to the air. So, it’s unlikely that vitamin C in skin creams offers much benefit. Vitamin E is believed to improve the appearance of scars and help speed wound-healing. But there’s no evidence that it does. And in some people, topical vitamin E causes allergic reactions.

Exfoliants

Aging skin often looks rough and sallow because it doesn’t slough off dead surface skin cells as easily as younger skin. Exfoliants help remove these surface cells. Two chemical exfoliants, alpha hydroxy acids and beta hydroxy acids, lower the skin’s pH level, which is believed to renew the skin more effectively than many scrubs, masks, soaps, toners, or abrasive cloths.

• Alpha hydroxy acids (AHAs). AHAs are obtained from fruits, including grapes, citrus fruits, and apples. Look for glycolic acid, lactic acid, malic acid, hydroxycaprylic acid, alpha-hydroxyoctanoic acid, triple fruit acid, or sugar cane extract on the label. AHAs can also cause skin irritation and may increase sensitivity to UV radiation. The FDA has cautioned consumers to use only products that contain an AHA concentration of 10% or less and a pH of 3.5 or more (lower pH numbers are more acidic), and to apply a sunscreen along with AHA-containing products.

• Beta hydroxy acids (BHAs). BHAs are chemically distinct from AHAs and are believed to be less irritating than AHAs. The most widely used BHA is salicylic acid, and like its relative aspirin, it has anti-inflammatory properties. It also doesn’t penetrate as deeply as AHAs do. Moreover, salicylic acid is more effective than AHAs for exfoliating oily areas of the skin, making it useful if you have oily skin or problems with adult acne. BHAs and salicylic acid can be found in many acne products at effective levels of 1.5%–2%. But anti-wrinkle products containing these ingredients tend not to list the percentage on their labels, so it’s difficult to know whether they contain sufficient amounts to be effective.

Retinoids

Vitamins don’t generally reduce wrinkles, with the exception of the topical vitamin A-based drugs called retinoids. Tretinoin, marketed as Retin-A and Renova, is the most common retinoid used in skin care. Introduced in the 1970s as an acne treatment, tretinoin demonstrated an ability to speed the turnover of superficial skin cells. In 1996, the FDA approved Renova, which contains a 0.05% concentration of tretinoin, as the first drug to treat wrinkles.

Tretinoin reduces fine lines and wrinkles by increasing the production of new collagen. It also stimulates the production of new blood vessels in the skin, which improves skin color. Additional benefits include fading “age spots” or “liver spots” (lentigines) and softening actinic keratosis. It takes 3–6 months of regular use before improvements in wrinkles are apparent, with best results after 6–12 months.

Several over-the-counter products containing retinoids, such as retinol, are now available. They may not be as effective in reducing wrinkles as tretinoin, but they do improve the appearance of photoaged skin. Tretinoin can be used with alpha hydroxy acids for additional skin-smoothing effects.

Is coconut oil healthful?

Q: I’ve read that organic coconut oil has health benefits. Could it improve lipid profiles if consumed every day?

A: I doubt that coconut oil has health benefits, especially beneficial effects on lipids, and I wouldn’t recommend that you consume it regularly.

For years, fat was portrayed as unhealthful. That’s not true. “Bad fats,” such as saturated and trans fats, are bad for you, but “good fats” — monounsaturated and polyunsaturated fats — actually have health benefits.

Saturated fats are a problem because they tend to increase LDL cholesterol levels, which in turn raises the risk of developing atherosclerosis and the heart disease and strokes that follow. True, they also tend to increase HDL (“good”) cholesterol, but not enough to compensate for the bad effects. Trans fats increase LDL and lower HDL, a double whammy.

Dietary oils — canola, corn oil, and so on — are all forms of fat. But unlike most other oils made from plants, coconut oil, as well as palm oil, are high in saturated fat. Saturated fat comes in several varieties; coconut oil is rich in one called lauric acid. Some groups and self-proclaimed experts are hawking lauric acid as a wonder food that will boost your immune system, help you lose weight, fight cancer — you name it. Needless to say, the evidence is weak to nonexistent. A respected nutrition textbook on our shelves does refer to the possibility of it having modest cavity-fighting properties. By contrast, there’s a great deal of evidence that, like other saturated fats, lauric acid increases LDL levels.

As with most dietary don’ts, there’s no need to be a prohibitionist. If you want to enjoy an occasional piña colada or a Thai curry dish, go ahead. I do. Coconut milk and oil are delicious. Just don’t kid yourself that they are good for you.

Is it a health mistake not to drink?

Q: I started drinking half a glass of red wine in the early evening, particularly pinot noir since it’s said to have a higher than normal concentration of resveratrol, generally adding blueberry juice to fill the glass. But I had to stop because I didn’t like the wine’s effect on me — slight problems with motor coordination, grogginess, and sleepiness. Should I be worried that so little alcohol had such a strong effect on me? Am I making a mistake by abandoning the use of alcohol, given its reputed health benefits?

A: Drinking moderate amounts of any type of alcoholic beverage — one drink a day for women, and up to two a day for men — does seem to lower the risk for heart disease and the most common type of stroke. Some doctors say that certain alcoholic drinks — red wine often comes up — are more heart-healthy than others because they contain more antioxidants like the resveratrol you mentioned. I’m not convinced, though, that any one type of alcohol-containing drink is superior to the others.

Moderation is the watchword here. Alcohol in greater amounts can cause many health problems, some related to the heart. For instance, it can weaken the heart muscle and help trigger abnormal heart rhythms.

People respond differently to alcohol. If just one small drink is giving you problems, then I’d have no reservations about giving up the habit. There are plenty of other ways that you can protect your heart and enhance your health overall: Get regular exercise; avoid saturated fat; and keep your weight down. And if you want to have a drink every day, go ahead and make it blueberry juice — straight up, no chaser — even though the heart-healthful effects remain unproven.

Anthony L. Komaroff, M.D., is editor in chief of the Harvard Health Letter, available at www.health.harvard.edu/health.

Do soy products cause thyroid problems?

Q: I read that soy can cause a low thyroid condition. What do you know about this?

A: Although many people consider soy to be part of a healthy diet, there have been persistent concerns about its effects on the thyroid gland. Animal studies dating back as far as 1959 have suggested that certain chemical components of soy — the isoflavones — may be linked to thyroid disorders, especially goiter and low thyroid. The two main soy isoflavones, genistein and daidzein, inhibit thyroid peroxidase, an enzyme necessary for making thyroid hormone. But luckily iodine blocks this antithyroid effect.

In 2003, a randomized clinical trial compared a daily dose of 90 mg of isoflavones with a placebo in 38 healthy postmenopausal women with normal iodine intake. After six months, there were no differences in thyroid function between the treatment and placebo groups. So soy shouldn’t cause thyroid problems as long as you get enough iodine in your diet.

Fortunately, that isn’t hard to do. The recommended dietary allowance (RDA) of iodine is 150 micrograms (mcg) per day. Two good sources of iodine include plants grown in iodine-rich soil and dairy products from animals that feed on such plants. Iodine-rich soil is found mainly on land that was once under salt water. But you needn’t worry if you don’t live near such an area, because you are almost certainly eating food from all over the country and all over the world.

Saltwater seafood, including deep-sea fish, shellfish, and even seaweed are also good sources of iodine. For example, a six-ounce portion of cod or haddock contains 200–250 mcg, and six ounces of shrimp have about 70 mcg.

In the United States, iodized salt is another major source. A half-teaspoon provides 134 mcg of iodine. If you avoid salt for health reasons, such as high blood pressure, or if you use non-iodized salt, you can still get your RDA from a daily multivitamin/mineral supplement. Read the label to make sure that it supplies 150 mcg.

Celeste Robb-Nicholson, M.D., is editor in chief of the Harvard Women’s Health Watch, available at www.health.harvard.edu/women.