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Surgery and Cosmetics

Everybody’s free to wear sunscreen

Camile Hexsel, Henry Lim

Tuesday, April 07, 2009

On August 2007, the Food and Drug Administration (FDA) published an amendment to the 1999 sunscreen monograph, with proposed changes in the current method of grading of ultraviolet (UV) B and UVA protection.1

UVB protection

Sun protection factor (SPF) is a measure of UVB protection, as it measures the ability of the sunscreen agent to protect the skin from erythema and edema, primarily an effect of UVB. Thus, in the 2007 amendment, the FDA suggests to change the acronym "SPF" to "UVB sunburn protection factor". Furthermore, a new grading system for UVB sunburn protection factor for sunscreen products was proposed, as the following four categories: low (SPF 2 to <15), medium (SPF 15 to <30), high (SPF 30-50), and highest UVB sunburn protection factor (SPF >50).

The FDA believes that there is no current data demonstrating the accuracy and reproducibility of specific SPF values over 50 and has therefore suggested a cap on the SPF of sunscreens to specific SPF values up to, but no greater than 50; sunscreen drugs with SPF greater than 50 would be labeled as 50+. 

UVA protection

In the United States, many sunscreen products are labeled as broad-spectrum UVB and UVA protection. However, objective grading of UVA protection is not required in the United States. In the 2007 amendment, the FDA suggests a new method of grading of UVA protection, which combines both an in vivo and an in vitro approach to grade UVA protection from low, medium, high to highest UVA protection, based on a star system that ranges from no star to 4 stars. The FDA proposes to use the persistent pigment darkening (PPD) method for in vivo UVA testing, and the ratio of UVA1 (340-400 nm) to total UV (290-400 nm) absorbance for in vitro testing.1,2 

Currently, only a select number of UVA sunscreen drugs approved by the FDA provide broad spectrum UVA protection, especially protection in the UVA1 spectrum.

In the 1999 FDA sunscreen monograph, avobenzone (butyl methoxydibenzoylmethane, Parsol 1789TM) and zinc oxide were included as approved sunscreen drugs.2-4 Subsequently, sunscreen products containing ecamsule (terephtalydene dicamphor sulfonic acid, Mexoryl SXTM) were approved by the FDA, the first one in July 2006.2,4,5

Avobenzone is the most effective long wavelength UVA1 filter currently available in the United States, with an absorption peak in the UVA1 spectrum (357nm).2,3,6 However, it is photo-unstable, and needs to be combined with other photostable sunscreens or stabilizers (eg, diethylhexyl 2,6-naphthalate, diethylhexyl syringylidene malonate).2

Opaque inorganic sunscreen actives may protect not only in the UVA range, but also against visible light. Decreasing the particle size into the micronized or ultrafine form for cosmetic acceptability shifts the protection towards shorter wavelengths. Microfine zinc oxide protects from the UVB to the UVA1 (340-400 nm) range; it is more effective in the UVA protection than microfine titanium dioxide, which protects in the ultraviolet B (UVB) and UVA2 (320-340 nm) range.2,6,7  

Ecamsule is a photostable sunscreen drug that absorbs in the short UVA range, with maximum peak absorption at 345 nm.2,6

Broad-spectrum and photostable UVB and UVA sunscreen actives, unavailable in the United States at the current time, include silatriazole (drometriazole trisiloxane, Mexoryl XLTM), bisoctrizole (methylene-bis-benzotriazoyl tetramethylbutylphenol, Tinosorb MTM), and bemotrizinol (anizotriazine, bis-ethylhexyloxyphenol methoxyphenol triazine, Tinosorb STM). Bisoctrizole and bemotrizinol are undergoing the FDA approval process.

Silatriazole is a photostable filter; it has absorption spectra in the UVB and UVA ranges, with absorption peaks at 303 nm and 344 nm.2,3,6 Bisoctrizole is a photostable sunscreen active with two maximum absorption peaks at 305 nm and 360 nm; it has both organic and inorganic properties as it consists of microfine particles that absorb, scatter and reflect UV.2,6 Bemotrizinol is a photostable UVA and UVB sunscreen active with maximum peak absorption at 310 nm and 343 nm.2,3,6

To ensure efficacy, adequate quantity of sunscreen should be applied. It is known that in actual use, most individuals apply 0.5-1 mg/cm2 of sunscreens, significantly less than the concentration used in FDA-mandated testing (2 mg/cm2); thus, in use SPF could be as low as 20 to 50% of the labeled SPF value.3 Therefore, for individuals with photosensitivity, sunscreens with minimum SPF 30 is advisable. Most newer formulation of sunscreens are photostable for a few hours of sun exposure. Substantivity, defined as the ability of a sunscreen to stay on skin surface, is affected by humidity, sweating, or simply rubbing.  Water-resistant sunscreens have good substantivity as they incorporate polymers that adhere to the skin.

Other photoprotection agents

Photolyase, a DNA repair enzyme, decreased UVB-induced DNA damage [cyclobutane pyrimidine dimers (CPDs) formation] by 40% to 45% in human skin when applied immediately after UVB exposure,3 resulting in prevention of  immunosuppression, erythema and sunburn formation.8 T4 endonuclease V is a bacterial DNA excision repair enzyme that repairs CPDs in DNA. As a topical treatment, it removes CPDs in DNA in the epidermis of animals and human beings.3 Topical application of T4 endonuclease V for 1 year decreased the rate of development of actinic keratoses and basal cell carcinomas.3,8

Antioxidants have been administered orally and topically for photoprotection in combination with sunscreens to enhance efficacy. Vitamin C and E reduce erythema, and sunburn cell formation. Vitamin E also reduces chronic UVB-induced photodamage and photocarcinogenesis.9

Green tea polyphenols exhibit anti-inflammatory activity, causing inhibition of UV -induced skin erythema, edema, and a decrease in the number of sunburn cells.10 Effects on photocarcinogenesis include a decrease in tumor burden, inhibition on the formation and size of malignant and non-malignant tumors and tumor regression in mice with established tumors. Effects of green tea polyphenols in photoaging include the inhibition of UVB induced expression of matrix metalloproteinases and reduction of UVB-induced collagen cross-linking.3

The plant extract Polypodium leucotomos (PL), available over the counter, does not have significant absorption in either UVB or UVA range, however, it increases the UV dose required for immediate pigment darkening, minimal erythema dose, minimal melanogenic dose and minimal phototoxic dose and down-regulates psoralen-UVA-induced phototoxicity and pigmentary and histological changes.3 In a study involving 26 patients with polymorphous light eruption and two patients with solar urticaria, oral PL (240 mg twice daily, started 15 days prior to sun exposure) has been reported to improve photosensitivity.11

In summary, for prevention of undesired effects of the sun, as well as for the management of photodermatoses, we recommend sunscreens with broad spectrum UVB (SPF 15 or above) and UVA protection, which include absorption in the UVA1 range. In the United States, products with photostabilized avobenzone, ecamsule, titanium dioxide and/or zinc oxide usually fulfill these criteria. In other parts of the world, products with the other aforementioned sunscreen actives with broad spectrum UVA protection that are not yet available in the United States are also recommended.


References

  1. 21 CFR Parts 347 and 352. Sunscreen drug products for over-the-counter human use: proposed amendment of final monograph; proposed rule. Fed Regist 2007;72:49070-49122.
  2. Hexsel CL, Bangert SD, Hebert AA, Lim HW. Current sunscreen issues: 2007 Food and Drug Administration sunscreen labeling recommendations and combination sunscreen/insect repellent products. J Am Acad Dermatol 2008;59:316-323.
  3. Kullavanijaya P, Lim HW. Photoprotection. J Am Acad Dermatol 2005;52:937-58; quiz 959-962.
  4. Sunscreen drug products for over-the-counter human use; final monograph. Food and Drug Administration, Health and Human Services. Final rule. Fed Regist 1999;64:27666-27693.
  5. The FDA approves new over-the-counter sunscreen. FDA Consum 2006;40:4.
  6. Tuchinda C, Lim HW, Osterwalder U, Rougier A. Novel emerging sunscreen technologies. Dermatol Clin 2006;24:105-117.
  7. Mitchnick MA, Fairhurst D, Pinnell SR. Microfine zinc oxide (Z-cote) as a photostable UVA/UVB sunblock agent. J Am Acad Dermatol 1999;40:85-90.
  8. Verschooten L, Claerhout S, Van Laethem A, Agostinis P, Garmyn M. New strategies of photoprotection. Photochem Photobiol 2006;82:1016-1023.
  9. Eberlein-Konig B, Ring J. Relevance of vitamins C and E in cutaneous photoprotection. J Cosmet Dermatol 2005;4:4-9.
  10. Afaq F, Mukhtar H. Botanical antioxidants in the prevention of photocarcinogenesis and photoaging. Exp Dermatol 2006;15:678-684.
  11. Caccialanza M, Percivalle S, Piccinno R, Brambilla R.  Photoprotective activity of oral polypodium leucotomos extract in 25 patients with idiopathic photodermatoses.  Photodermatol Photoimmunol Photomed 2007;23:46-47.
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