Antioxidants beef up broad-spectrum sunscreen
SPF corresponds primarily to the UVB portion of the solar spectrum and erythema, but not with UVA, UV-induced oxidative stress or immune suppression, says Mary Matsui, Ph.D., executive director, Clinique Laboratories.
Therefore, she says, "Reliance on SPF is not enough to ensure complete protection against the full spectrum of UV radiation. Antioxidants can add protection against 'unseen' damage."
To test this proposition, researchers enlisted 15 Chinese women (Fitzpatrick III skin type), undertaking their research in winter to minimize the effect of environmental sun exposure. First, researchers determined the volunteers' minimum erythemal dose (MED), which was between 40 and 60 mJ/cm2, with an average of 50 mJ/cm2.
Researchers then marked six rectangular regions on each volunteer's non-exposed upper back — one for control purposes (which was never exposed to UV) and one for each of the following materials: sunscreens plus antioxidants (caffeine, vitamin E, vitamin C, Echinacea pallida, gorgonian extract and chamomile essential oil); sunscreens only; antioxidants only; vehicle control; and untreated (no vehicle).
For four consecutive days, researchers exposed these five sites on the non-exposed upper back to 1.5 MED solar-simulated radiation (ssUVR). The sixth site was sham irradiated. Throughout the trial, investigators were blinded to the identity of test materials, which they applied 30 minutes before each UV exposure and six, 24 and 48 hours afterward. Three days after the last exposure, investigators took skin specimens by punch biopsy from the six sites after recording the sites' melanin index (MI) and erythema index (EI) using a colorimeter (Mexameter MX 18, Courage & Khazaka Electronic GmbH).
They found that irradiated sites that received antioxidants only, vehicle and no treatment at all showed a tanning response, while sites treated with sunscreen plus antioxidants or sunscreen only did not respond with pigmentation, Dr. Matsui says.
The sites treated with sunscreens only or sunscreens plus antioxidants were also protected best against sunburn, although the site treated with antioxidants showed some decrease in UV-induced erythema, she adds.
Researchers measured the effect of treatments on Langerhans cells by measuring CD1a positive cell counts using both ABC techniques and fluorescence staining. In this cutaneous immune function endpoint, Dr. Matsui says sunscreens and antioxidants together completely prevented Langerhans cell depletion (p<0.001), whereas neither component proved effective alone.
"Probably the most interesting and surprising finding was that antioxidants could provide added benefits even when there were broad-spectrum sunscreens (SPF 25) in the formula with some degree of UVA protection," Dr. Matsui says .
This also indicates that relatively low levels of UV could also damage skin, she adds. Additionally, she says that although researchers didn't test the antioxidants separately in vivo, extensive in vitro testing has shown that each has efficacy primarily for specific reactive oxygen species (such as superoxide radicals, hydrogen peroxide and singlet oxygen). Thus, researchers believe them to be complementary.
Another unique aspect of the study was its reliance on multiple UV exposures rather than one, Dr. Matsui says.
"This has become a point of interest to photobiologists," she says, "as we are finding that this more 'real-world' exposure pattern may yield different results than the current standard of testing."
Overall, she says the study "should be a wake-up call for development of better sun-protection materials and a better method of measuring protection."
Disclosure: Clinique Laboratories sponsored 50 percent of this study.
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