Ultraviolet Protection with Cosmeceutical Ingredients

While both zinc oxide and titanium dioxide are popular ingredients, a recent study from Université de Nantes, France, tested the efficacy of zinc oxide and titanium dioxide-infused products, determined by an in vitro method using a spectrophotometer equipped with an integration sphere.⁴ Researchers determined titanium dioxide was "much more effective than zinc oxide; indeed no commercial form of zinc oxide tested can give a sun protection factor (SPF) higher than 10 at its maximum dose of use, unlike titanium dioxide which in its coated form (coated with alumina and with stearic acid, amongst others) gives a SPF of 38." In contrast, a study from Duke University claimed zinc oxide is a superior sunscreen.⁵ Researchers compared microfine zinc oxide and microfine titanium dioxide for their abilities to attenuate UVA radiation and relative whiteness in cosmetic formulations. UVA attenuation was measured by diffuse reflectance spectroscopy on normal human skin in vivo. Whiteness was determined by reflectance density of dried coatings on a black background of the two particulates at varying concentrations. The study concluded microfine zinc oxide "demonstrates superior protection compared to microfine titanium dioxide in the UV spectrum between 340 and 380 nm, while microfine zinc oxide is less white than titanium dioxide at all concentrations."

The New "SPF" Frontier

A newer sunscreen ingredient that is quickly gaining popularity is avobenzone, a dibenzoylmethane derivative and an oil soluble ingredient used to absorb the full spectrum of UVA rays. According the American Academy of Dermatology (AAD), avobenzone absorbs UVA radiation before it penetrates the skin, thereby protecting the skin from oxidative damage. While avobenzone was not photo stable when it was first introduced, new formulations have been created that contain a combination of antioxidants, allowing for a stable formula. One avobenzone formulation that was approved as sunscreen by FDA in 2006 contains ecamsule, octocrylene and oxybenzone, antioxidants that help stabilize avobenzone and provided long-term UVA protection. Another formula that was approved in 2007 contains a photostabilizing solvent that absorbs UVA radiation, diethylhexyl 2,6-naphthalate (DEHN). "Avobenzone is a valuable sunscreen ingredient that delivers proven UVA protection that, until now, had not been offered in sunscreen formulations in this country," said Zoe D. Draelos, M.D., at the 2007 AAD’s Summer Academy Meeting.⁶ "Sunscreens that contain the photostable forms of avobenzone are excellent choices when selecting a cosmeceutical with anti-aging properties."

At the meeting, Draelos also stated green tea is generating buzz in the cosmeceutical industry. However, when used in cosmeceutical products, an antioxidant must be added in order to stabilize the green tea, butylated hydroxyl-toluene (BHT). Draelos reported on an animal study that replaced laboratory water with green tea in a mouse colony.⁷ Two groups of 6- to 7-week old female SKH-1 hairless mice were UVB irradiated (180 mJ/cm²) three times each week for 24 weeks. One group consumed water and the other drank water containing 2 g/L green tea polyphenols (GTP). The control group drank water and was not exposed to UVB radiation. UVB-induced tumors and skin biopsies from the control group were analyzed. Oral administration of GTPs reduced UVB-induced tumor incidence (35 percent), tumor multiplicity (63 percent) and tumor growth (55 percent). The GTPs+UVB group had reduced expression of the "matrix metalloproteinases (MMP)-2 and MMP-9, which have crucial roles in tumor growth and metastasis," and enhanced expression of tissue inhibitor of MMP in the tumors compared with mice that were treated with UVB alone. It was concluded that researchers "found the animals had decreased sunburn cells following exposure to UVB radiation."

A similar study from the Susan Lehman Cullman Laboratory for Cancer Research, New Jersey, subjected female SKH-1 hairless mice with UVB (30 mJ/cm2) twice a week for 10 to 20 weeks, resulting in the formation of a large number of cellular patches which were considered putative early cellular markers for tumor formation.⁸ The number and size of the patches increased progressively with continued UVB treatment. Discontinuation of UVB for four weeks resulted in an 80 to 90 percent decrease in the number of patches. The number of the remaining patches did not decrease any further but remained relatively constant for four to nine weeks. Oral administration of green tea (6 mg tea solids/ml) or caffeine (0.4 mg/ml) as the sole source of drinking fluid during irradiation with UVB, twice a week for 20 weeks, inhibited UVB-induced formation of patches by approximately 40 percent. Furthermore, oral administration of green tea (6 mg tea solids/ml) as the sole source of drinking fluid or topical applications of caffeine (6.2 micromol) once a day, five days a week, starting immediately after discontinuation of UVB treatment, enhanced the rate and extent of disappearance of the patches.