Photo: Plasma connects to different magnetic polarities on the sun. Courtesy Wikipedia.
If you can only buy one anti-aging product, then buy a broad-spectrum (UVA/UVB) sunscreen of at least SPF 30, and use it each and every day. Your skin will thank me in twenty years, as UV exposure has been linked to almost every known cause of aging, from free radical release to matrix metalloproteinase formation to DNA damage, and ultimately, to signs of aging that include sunspots, wrinkles, and collagen loss.
The best sunscreens block UV light in the UVB range (280-315 nm), as well as the UVA range (320-400 nm). A clever mnemonic for UVB and UVA is that UVB causes burning (erythema), whereas the longer-wavelength UVA penetrates skin deeper, causing signs of aging, although UVB also contributes to aging, as it induces matrix metalloproteinase activity. At any rate, according to Dr. Leslie Baumann, author of Cosmetic Dermatology, the Sun Protection Factor (SPF) commonly listed on products refers to the amount of UVB protection, measured by the time it takes for a person without sunscreen versus a person with sunscreen to show a erythemal skin reaction (i.e., to show redness). The amount of UVB an SPF is effective at blocking may be estimated using the following algorithm from Dr. Rachel Herschenfeld: SPF 30 allows 1/30 UVB rays, or 3.3% through, meaning it blocks about 96.6% of UVB rays; SPF 50 allows 1/50 UVB rays, or 2.0% through, meaning it blocks 98.0% of UVB rays.
At this time, products in the U.S. do not quantify the amount of UVA protection in a product. In Europe, the IPD (immediate pigment darkening assay) and the PFA or PPD (persistent pigment darkening assay) are used to assess UVA protection. In a 2004 study by Moyal, it was demonstrated that products containing Mexoryl (chemical name Ecamsule) had higher UVA protection than sunscreens without Mexoryl. Mexoryl, available as SX (water soluble) and XL (lipid soluble), is very effective for two reasons: one, it is very stable [as a benzylidene camphor derivative], and two, because it undergoes photoisomerization, followed by photoexcitation, which means that it causes for UV light to be released as thermal energy rather than allowing for UV light to be absorbed into the skin and cause damage. Additionally, Mexoryl SX and Mexoryl XL are even more stable than each alone; however, Mexoryl XL is often too oily for some sensitive skin. Until FDA approval in 2006, Mexoryl was not available in the U.S., and many who knew of their high PD and PPD ratings from Europe ordered products (like LaRoche Posay Anthelios SX, $29.00, Dermstore.com) with Mexoryl SX online. However, the coveted ingredient is today available in the U.S. in sunscreens by L’Oreal, such as L’Oreal Dermo-Expertise Revitalift UV Daily Moisturizing Cream with Sunscreen ($21.99, Drugstore.com). Additionally, Neutrogena has released a multitude of sunscreens with Helioplex, a stabilized, patented combination of oxybenzone and avobenzone that has been demonstrated in clinical tests to provide longer-lasting UVA protection than most other sunscreens. In comparing mexoryl and Helioplex, Neutrogena Ultra Sheer SPF 70 has been reported to have a PFA value of 23.3 or 26.5, interestingly higher than the reported PFA value of 10 for Mexoryl SX and XL in combination. Therefore, based on the current reported PFA data, it seems that Neutrogena Ultra Sheer SPF 70 ($17.15 for two, Amazon.com) is even more effective than Mexoryl, providing the best UVA protection on the U.S. market.
However, proper application may be as important as the right product. A 1997 study by Stokes et al. cited by Baumann in Cosmetic Dermatology found that most users achieve a mean SPF of between 20 and 50 percent of that expected from the product label, because they do not apply the sunscreen as thickly as in laboratory conditions (2 mg/square centimeter of skin, or 30 mL of sunscreen over the average human body). Baumann instructs patients to estimate their UVB protection by multiplying the SPF by one-third; therefore, a product of SPF 60 grants the average user about twenty times their natural time in the sun before burning. Another caveat with sunscreen use: improper application time. Users need to be aware that sunscreens need to be applied at least 30 minutes before sun exposure, and, for proper protection, re-applied every two to three hours from the initial application, or sooner, if being exposed to the water.
“Waterproof” is additionally a term that misleads consumers into believing they have more sun protection than they really do. According to Baumann, “waterproof” sunscreens are those that endure laboratory tests consisting of 20 minutes of swimming, followed by a drying period, followed by an additional 20 minutes of swimming. “Very waterproof” sunscreens only endure an additional 20-minute drying period, another 20-minute swimming session, a third 20-minute drying period and a final 20-minute swimming session. Therefore, spending an entire day at the beach, even with a “very waterproof” sunscreen, does not provide effective sun protection beyond two to three hours.
A third mistake consumers make is using expired sunscreens. Expiration dates on sunscreens are not featured if the products are stable for three years. For this reason, consumers should toss out sunscreens or products containing sunscreen of questionable age.
Therefore, consumers need to be aware that UVA protection is not measured on sunscreen labels in the United States, whereas SPF provides a factor of the amount of time a person can stay in the sun before experiencing a burn. Additionally, sunscreen users need to be aware that sunscreen must be applied 30 minutes prior to sun exposure, that no sunscreen is truly “waterproof” beyond two to three hours, and that even sunscreens without expiration dates only last up to three years. Come back tomorrow for more information on sun protection in Sunscreen, Part II: Physical versus Chemical, Alternatives, and Possible Detriments. 🙂