With the outdoor season in full swing across the Northern Hemisphere, everyone's thoughts should turn to sun protection. That means you, whether you have light or dark skin, have blue or brown-black eyes, always sit in the shade, or often play or bask in the sun.

True, sunshine restores the soul, fosters the formation of vitamin D and helps plants grow. But no one is safe from its damaging ultraviolet rays. Getting a tan or using a tanning product that dyes the skin temporarily offers minimal protection against sun damage.

And true, 80 percent of UV damage from sun exposure occurred in childhood and adolescence, when we older folks knew nothing about sunscreen, sometimes suffered scorching sunburns, or lay in the sun slathered in oils to enhance tanning. But at every age, there are steps to take now that can minimize the harm done decades ago and prevent new problems.

Everyone should be replacing misinformation with facts about the effectiveness of sunscreens and sun-protective clothing, and then putting those facts to proper use.

The Right Priorities

How important is this? Very. More than a million cases of basal cell or squamous cell cancers are diagnosed annually in the United States. And while most of these are highly curable, they typically occur on exposed areas of the body—face, neck, arms and hands—and their treatment can leave noticeable scars or whitish spots.

Also, another form of skin skin cancer, melanoma, sometimes related to sun damage, is not so curable. About 62,000 cases of melanoma will be diagnosed this year, and more than 7,900 people will die of this cancer, which has been increasing in incidence by about 3 percent a year since 1980.

More myths than facts abound about sunscreens. And more people misuse them than use them properly.

First, there is no evidence that the use of sunscreen increases the incidence of skin cancer. Nor is there evidence that regular use of sunscreens can cause internal damage. These are surface agents only; they don't get inside cells or penetrate deep into the skin.

True, sunscreens reduce the body's ability to form vitamin D. About 15 minutes of sun a day in summer on unprotected face and arms can result in a year's supply in people under 65. But at any age, this essential nutrient is more safely obtained from foods and vitamin supplements.

Most sunscreens protect against both ultraviolet B radiation, which causes sunburns, and ultraviolet A radiation, which ages the skin. Both types have been implicated in skin cancer. But the S.P.F. rating (for sun protection factor) relates only to UVB exposure.

If a person who would get sunburned without protection in 20 minutes uses a product with an S.P.F. of 10, that burn should not occur until spending 200 minutes in the sun, assuming the sunscreen is slathered on properly.

What is proper slathering? The use of one ounce of a product on an average body wearing an average bathing suit. However, most people use less than half this amount, which would significantly reduce the protection factor.

Dermatologists recommend the routine daily use of a sunscreen with an S.P.F. rating of 15 or higher on all exposed areas—whether the day is sunny or cloudy and skin is light or dark. UV radiation readily penetrates cloud cover.

Those with fair skin and anyone who has already had skin cancer should use a sunscreen with a protection factor of at least 30, which blocks more than 97 percent of the sun's rays. The higher the number, the better; the added protection is real but very small.

The Right Stuff

But remember, the protection factor is only part of the story. A product with an S.P.F. of 30 may have a UVA protection rating of only 2. Your sunscreen should be a broad-spectrum one that also blocks UVA radiation. Two ingredients now used in "complete" sunscreens in cosmetically acceptable micronized forms are titanium dioxide and zinc oxide.

Two other agents that offer broad-spectrum protection, Mexoryl and Tinosorb, help to stabilize UVA protection during prolonged exposures. They are available in Canada and Europe but have not yet been approved by the Food and Drug Administration here.

Neutrogena, however, has a new product on the American market, Ultra Sheer, with an S.P.F. of 55, that is said to do the job of Mexoryl. It is also more affordable and is cosmetically comfortable. The company uses a patented Helioplex technology to stabilize two UV blockers, avobenzone and oxybenzone.

Because sunscreens must react with the surface of the skin to be effective, they should be applied 15 to 30 minutes before going out in the sun. Most products should be reapplied every two hours (one application of Ultra Sheer is supposed to remain effective for six hours or longer).

Swimmers and those performing intense physical activity should use a water-resistant or very water-resistant sunscreen. But all sunscreens, whether water-resistant or not, should be reapplied after swimming or profuse sweating.

And don't forget to use enough: one ounce, the amount in a shot glass, should be used to cover exposed skin in summer.

Sunscreens should be used by everyone over the age of 6 months. Younger infants should be kept out of the sun at all times; use sunscreen on them only in rare situations when sun exposure is unavoidable.

The Right Clothes

As with sunscreens, there are mistaken beliefs about clothing. Most summer clothing offers minimal protection, according to Dr. Susan H. Weinkle and Harriet Lin Hall, writing in The Skin Cancer Foundation Journal. A wet T-shirt on a swimmer provides at best an S.P.F. of 3; dry, the shirt offers on average a factor of 7.

Most protective are tightly woven fabrics in dark colors—not your usual summer attire. A green cotton T-shirt, for example, may have a protection factor of 10, while a long-sleeved dark denim shirt has a factor estimated at 1,700.

But there are now excellent clothing options for sun-sensitive people, if they can afford them. Several companies now make shirts, pants, hats and other garments from sun-protective fabrics that are lightweight and breathe and are reasonably comfortable to wear in hot weather.

Sun Precautions was the innovator, with its Solumbra line, which blocks more than 97 percent of UVA and UVB. A Solumbra shirt and hat are ideal for boaters and hikers. The garments are sold in stores or through the company's catalog (1-800-882-7860). They retain their protective properties through at least 100 washings.

Another less expensive option is to wash your clothes with SunGuard, a product produced by Rit that treats fabric with Tinosorb and offers 96 percent UV protection. One treatment retains its protective value through about 20 washings.

In addition to skin, eyes should be protected against UV damage. You need not spend very much to get sunglasses with 100 percent UV protection in a wraparound style. And not just for adults. Children need them, too.

Of course, the best option is to keep your entire body covered with clothing and wear a large-brimmed hat and sunglasses when out in the sun. This is not exactly standard beach attire, leaving the option of a generous coating of high-S.P.F. sunscreen and use of a beach umbrella.