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Ask the doctors

Q. I have terrible dandruff that just doesn't seem to ever clear up. What can I do to treat it?

A. For most people, using a dandruff shampoo once or twice a week can control this annoying condition, in which the skin on the scalp becomes dry and flakes off. But in some cases, the condition doesn't clear up and actually requires medical attention.

Eczema is an itchy rash that's often hard to get rid of. Most people can't help scratching it, which further irritates the skin. Eczema is often, but not always, related to allergies. A common cause is your skin overreacting to everyday irritants, such as dust, soaps and detergents, or even dry, cold air, which triggers an intensely itchy allergic reaction.

Skin affected by eczema becomes dehydrated and dry easily, so treatment involves rehydrating the skin. Baths and showers must be short and not too hot. Afterwards, gently pat your skin dry and promptly apply moisturizers while your skin is still moist. Thick creams that lock in the moisture help the most. Be sure to choose creams or lotions without fragrances or preservatives. Limit the use of soaps and shampoos, too. These products remove the skin's natural oils and worsen dryness. And over-the-counter oral antihistamines can help with the ferocious itch.

A widely-advertised facial moisturizer claims to be the best on the market � and sells for $225 per bottle. Should you buy it? Another brand offers a complete skin care regimen � but it comes in 10 different bottles of lotions and potions that all need to be applied daily. Is it worth your time?

Despite manufacturers' claims, many cosmetic products will remove more cash from your wallet than dirt and oils from your skin. You don't need an expensive or lengthy skin care routine � and the good news is, the most effective and reliable regimen is also quick and inexpensive.

Learn to spot an actinic keratosis before it becomes cancerous.

About 58 million people have at least one actinic keratosis (AK), a precancerous skin growth caused by too much sun exposure.

Yet most people don't see the potential danger in these lesions because they are small, with few if any annoying symptoms, and can go away almost as fast as they appear.

On call

Q. Is there any difference between sunstroke and heatstroke and are there certain signs and symptoms I should look for?

A. These two terms refer to the same condition. Heatstroke (or sunstroke) happens when the body can no longer maintain a temperature of under 105° F when exposed to hot weather. People almost always have warning symptoms before heatstroke, yet sometimes they do not pay attention, or are not able to take action.

The first accurate medical discussion of psoriasis dates back to 1801, but the disease itself is much older. In fact, its very name is borrowed from an ancient Greek word meaning an itchy or scaly condition. About 7 million Americans are plagued by this itching and scaling, and many of them have serious complications involving other organs. Although psoriasis is classified as a dermatologic disease, it doesn't start in the skin, and its damage may be more than skin deep.

Beneath it all

At a basic level, psoriasis is a disorder of the immune system. White blood cells called T-helper lymphocytes become overactive, producing excess amounts of cytokines, such as tumor necrosis factor, interleukin-2, and interferon-gamma. In turn, these chemicals trigger inflammation in the skin and other organs. In the skin, the inflammation produces three characteristic findings: widened blood vessels, accumulation of white blood cells, and abnormally rapid multiplication of keratinocytes, the main cells in the outer layer of the skin. In healthy skin, keratinocytes take about a month to divide, mature, migrate to the skin surface, and slough off to make way for younger cells. But in psoriasis, the entire process is speeded up to as little as three to five days. The result is thickened, red skin that sheds silvery scales of keratinocytes that have matured before their time (see Figure 1).

Q. I'm 63, and I've begun to notice a decline in the quality of my fingernails. They have numerous up-and-down ridges, and at the tips, they're always splitting. I've heard you can tell a lot about a person's health from the condition of her nails. What does my split nails say about mine?

A. Some changes in nails can be a sign of an underlying health problem, but the lengthwise nail ridging you describe is usually not one. It's simply a common sign of normal aging. The growth of fingernails and toenails slows as we get older, and their appearance may change. Some nails become yellowed or dull and brittle, and some or all may develop tiny longitudinal ridges. Fingernails tend to become thinner and more fragile, while toenails usually become thicker and harder.

Research we're watching

If your hair has been thinning, an infusion of your body's own plasma may help grow it back, according to the American Academy of Dermatology.

A number of recent studies show that platelet-rich plasma (PRP) therapy is successfully regrowing lost hair. This includes a 2018 study in the International Journal of Women's Dermatology that found the technique was beneficial in treating androgenetic alopecia, a type of genetically and hormonally driven hair loss that affects as many as 35% of women by age 60.