Skin cancer due to sun exposure is a continuous, cumulative process, with approximately 53% of skin cancer-related deaths occurring after 65 years of age. occurring after 65 years of age. For many people, sunscreen is their main line of defense against skin cancer, as well as sunburn and aging (e.g., roughness, wrinkles, "age" or "liver" spots, dilated blood vessels). Today, SPF (Sun-Protection Factor) is the most widely used guide to sunscreen selection. Understanding the limitations of SPF will make us better informed (and better protected) consumers.

Developed as a research tool, SPF is defined as how long you can stay in the sun without burning from ultraviolet B (UVB) light. In theory, if your skin burns within 20 minutes of exposure to the sun, SPF 15 sunscreen protects you 15 times longer, or about 5 hours.

That’s the theory; however, SPF suggests precision that’s impossible to achieve outside the laboratory. In the real world the ability to tolerate sun exposure is influenced by skin type, duration of exposure, and intensity of sunlight, which changes throughout the day.

The value of SPF is also limited because conventional sunscreens block UVB, and “broad-spectrum” sunscreens protect against UVB and ultraviolet A (UVA). However, visible light and infrared radiation — 90% of solar radiation — also affect the skin in the same way as UVA. Available sunscreens don’t protect from infrared and visible wavelengths.

The bottom line

None of this is meant to suggest that SPF is useless, but its value as a tool to protect aging skin from the toxic effects of sunlight is limited. Comprehensive skin protection includes more than sunscreens in order to protect skin from the sun’s rays.

New FDA requirements for sunscreens sold over-the-counter

As we grow older, skin becomes thinner, sags, and wrinkles. It injures more easily and heals more slowly. For many people, sunscreen is the keystone for skin protection. Now, the U.S. Food and Drug Administration (FDA) has updated their sunscreen rules, summarized here.

What is SPF?
SPF (sun protection factor) measures protection from sunburn caused primarily by ultraviolet B (UVB) rays. Higher SPF values suggest greater protection.

What are the limitations of SPF?
SPF doesn’t adequately measure protection from ultraviolet A (UVA) rays. In addition, both infrared light and visible light contribute to the development of fine lines, wrinkles, and uneven skin tone. These effects are not included in the SPF rating.

Is it worthwhile to buy sunscreens with SPF higher than 50?
No. According to the FDA, there is insufficient evidence that SPF values higher than 50 provide greater protection than products with SPF 50.

What is a “Broad Spectrum” sunscreen?
Sunscreen products that pass the FDA's test for protection against both UVA and UVB rays may be labeled “Broad Spectrum."

Why are sunscreens no longer labeled as “waterproof”?
FDA-ordered changes in sunscreen labels prohibit the terms "waterproof," "sweat-proof," and "sunblock." If a sunscreen product is water resistant, it can be stated on the label with the amount of time between applications (40 or 80 minutes).

Do sunscreen products protect against skin cancer?
Broad Spectrum sunscreens with SPF of at least 15 may state they reduce the risk of skin cancer and early skin aging when used as directed with other sun protection measures. Sunscreens that don’t carry the Broad Spectrum label, or that do but have an SPF between 2 and 14, may claim only to help prevent sunburn.

How often must I apply sunscreen?
Reapply sunscreen at least every 2 hours or according to the directions on the label.

What’s the best strategy for protecting myself from the negative effects of sun exposure?
Regularly use a Broad Spectrum sunscreen with an SPF value of at least 15 combined with other protective measures. These include limiting time in the sun, especially between 10 AM and 2 PM; wearing clothing to cover skin exposed to the sun (long-sleeved shirts, pants, sunglasses, and broad-brimmed hats); and using a water resistant sunscreen if swimming or sweating.