In Woody Allen’s classic “Annie Hall,” Alvy Singer laments, “Everything our parents said was good is bad.” He lists whole milk and red meat as two offenders.

He also includes the sun. Now, calling the sun “bad” is obvious exaggeration (the earth can’t exist without it), but the truth about sun exposure is much more complex than believed in the 1920’s when fashion giant Coco Chanel decreed tanning “in.” For decades after Coco returned to Paris bronzed from Cannes, a suntan was seen as the picture of health. However, waves of research have refined our knowledge of the sun’s ultraviolet rays (UVR). Here, guided by our Photobiology Committee (our panel of experts on UV exposure), we explore some stubborn myths about tanning and UV that have recently been shot down.

Tanning is beneficial, because it helps prevent sunburn. Darker skin does offer greater protection than light skin against sunburn and skin cancer. However, that applies only to people with naturally darker skin. Tanning, like sunburns, attacks the skin’s DNA, producing genetic defects that may cause skin cancer.

Ultraviolet B (UVB) rays are the only carcinogenic UV rays. Scientists divide the solar UV spectrum into three wavelengths — UVA, UVB and UVC. Once, UVA (long wavelengths of 320-400 nanometers, or nm) and UVC (the shortest, highestenergy UV, under 290 nm) were thought harmless, and only UVB (middle-range UV of 290-320 nm) was believed dangerous. UVC is still deemed no threat, since it is sufficiently absorbed by the ozone layer. But UVA accounts for up to 95 percent of solar UVR reaching Earth. Though far less capable of causing sunburn than UVB, it is present during all daylight hours yearround, while the amount of UVB in sunlight varies by season, location and time of day. And unlike UVB, UVA can penetrate glass.

By the 1990’s, scientists knew that UVA exacerbates the cancer-causing effects of UVB, and is the main wavelength behind photoaging. In the past two years, an Australian-U.S. study found that UVA may be more carcinogenic than UVB. It penetrates more deeply and causes more genetic damage in the skin cells (keratinocytes) where most skin cancers arise. The National Institutes of Health and the World Health Organization now designate both UVA and UVB as causes of human cancers.

Tanning beds are safer than sun exposure. Tanning salon owners say tanning machines are safer than suntanning for two reasons: 1) they mainly use UVA rays, and 2) they offer more “controlled” UV exposure. However, the new research on UVA damage kills the first argument, and studies have revealed that tanning salons frequently exceed “safe” UV limits. Study after study has shown that sunbed tanning increases the risk of both melanoma and nonmelanoma skin cancers.

The higher a sunscreen’s SPF, the greater its protection. True, higher SPFs are more protective than lower ones. The Skin Cancer Foundation maintains that to be effective, sunscreens must be SPF 15 or higher. However, SPF rating only specifies protection from UVB. For adequate protection against both UVA and UVB, you need “multispectrum” or “broad-spectrum” UVA/UVB protection—not just a high SPF. The label should list an FDA-recognized UVA screening agent such as avobenzone (Parsol 1789), zinc oxide or titanium dioxide. Some newer UVA screening agents, such as Mexoryl, already used in Europe but not yet FDA-approved, appear more stable in the sun and may provide even greater UVA protection than avobenzone, zinc oxide, and titanium dioxide.

Once you’ve applied an effective sunscreen, you’re safe to stay outside. Actually, sunscreens lose effectiveness after awhile; reapply after about 1 1/2 hours, and immediately after sweating heavily or swimming. Plus, no matter how well you apply sunscreen, some UV gets through to your skin. A broad-spectrum SPF 15+ sunscreen should be considered part of a comprehensive sun safety program that includes these strategies:

• Seek the shade, especially between 10 AM and 4 PM
• Cover up with clothing, including a long-sleeved shirt and long pants
• Wear a broad-brimmed hat and UV-blocking sunglasses
• Apply sunscreen liberally on all exposed areas. Use two ounces total, about equivalent to the size of a golf ball.