But these rules will not take effect for another year (and for small manufacturers, two years). Meanwhile, everyone needs to know what to do now about preventing painful sunburns, disfiguring and deadly skin cancers and premature skin aging.

How high an SPF should one choose? Is SPF 60 really that much better than SPF 30? What does “broad spectrum” mean? Are all sunscreen ingredients equally effective? And equally safe?

And perhaps the most frightening question: Why has the incidence of melanoma, the deadliest of skin cancers, doubled since sunscreens (as opposed to tanning lotions) became popular?

No better time to get the answers to these questions than now, the week of the summer solstice. Even if it is not sunny where you are, the ultraviolet rays hitting your skin will be their most intense.

Rating Sunscreens

First, some facts about sun and current sunscreen labels. There are two kinds of solar rays: short ones called UVB that cause burning and skin cancer and long ones called UVA that cause skin cancer and wrinkling. SPF ratings — the letters stand for sun protection factor — reflect only the extent of protection against UVB. The higher the rating, the longer one can stay in the sun before burning.

But there are two important caveats. First, SPF ratings are based on a rather thick application of sunscreen, not the amount consumers normally use, which is most often a quarter to a half the amount applied in manufacturers’ tests. An adult in a bathing suit should apply about three tablespoons of lotion every two hours, experts say.

Second, above an SPF of 30, which can block 97 percent of UVB (if used in testing amounts), effectiveness increases by only 1 or 2 percent. In the way that sunscreens are used in the real world, then, a product with an SPF of 30 actually provides the protection of SPF 2.3 to 5.5, and one rated SPF 50 provides the protection of SPF 2.7 to 7.1, according to a report published this month in Drug and Therapeutics Bulletin.

UVA, which represents more than 95 percent of solar radiation reaching the earth, does not figure in SPF ratings. The phrase “broad spectrum” is meant to indicate protection against UVA, but there is no numerical rating for product effectiveness. Under the new rules, products labeled “broad spectrum” will have to provide equal protection against UVB and UVA, and only products with an SPF of 15 or higher will be allowed to claim protection against skin cancer and premature skin aging.

Meanwhile, dermatologists suggest choosing only products that are labeled “broad spectrum” and have an SPF rating of 30 to 50. There is no evidence that anything higher than 50 is any better. Apply the sunscreen just before exposure, and reapply it two hours later — it loses effectiveness over time. And even if the label claims the sunscreen is water resistant, be sure to reapply it after swimming or sweating heavily.

The rise in melanoma has led to fears that sunscreens may actually cause this deadlycancer. But other explanations are more likely. By allowing people to stay in the sun longer, sunscreens have greatly increased exposure to UVA radiation. And many, if not most, victims of melanoma were damaged long before sunscreens became popular. A history of sunburn is a major risk factor for this cancer; five sunburns per decade raise the risk by about threefold.

Another reason for the increase in diagnoses: skin cancer screening and detection have improved greatly in recent decades.

With regard to ingredients, many dermatologists recommend products with micronized titanium or zinc oxide as the most effective sun blockers that leave no white residue on the skin. There is some concern, based on animal studies, that the most popular ingredient in sunscreens, oxybenzone, may disrupt natural hormones, but the scientific evidence is scant.

Another chemical, retinyl palmitate, sometimes listed among the inactive ingredients, has been linked to skin cancers in animal studies. Because it is converted into a compound that can cause birth defects, it should be avoided by women who are pregnant or likely to become pregnant.

However, although more studies of these possible risks should be done, Consumer Reports concluded that “the proven benefits of sunscreen outweigh any potential risks.”

Finally, don’t be fooled by price. In tests of 22 sunscreens, Consumer Reports found nine to be effective against UVB and UVA and ranked three as “Best Buys”: Up & Up Sport SPF spray (88 cents an ounce) at Target; No-Ad With Aloe and Vitamin E SPF 45 lotion (59 cents); and Equate Baby SPF 50 lotion (63 cents). The organization said La Roche-Posay Anthelios SPF 40 cream, at $18.82 an ounce, scored well below these three in effectiveness.

Although it may be tempting to try to kill two birds at once with a combination sunscreen and insect repellent, the Centers for Disease Control and Prevention does not recommend this. Multiple applications could result in an overdose of the repellent.

Seek Other Protection

The best advice to prevent UV damage is to stay out of the midday sun altogether and to cover up with clothing, a hat and umbrella during the rest of the day even if it is cloudy. Clouds do not block damaging rays.

Keep in mind that ultraviolet radiation is reflected off sand and water, intensifying exposure even if you are protected by an umbrella from above.

Ordinary clothing provides a good sun shield when dry (the tighter the weave, the better) but little or no protection when wet. Special sun-protective clothing is costly but works well wet or dry; it is a wise investment for children who tend to stay in or around water for hours. Caps with a neck flap are especially helpful for sports enthusiasts. And no matter how well covered up you are, don’t forget to apply sunscreen to your face, ears, neck and hands.

Also, keep in mind that some sun exposure is necessary to maintain a healthful level of vitamin D. Dermatologists suggest, for light-skinned people, that exposing one’s hands, arms, face or back to nonburning doses of sunlight for 15 minutes two or three times a week from April to September should result in adequate vitamin D synthesis. Dark-skinned people need longer exposure.