Update on Sunscreens

Protection Against Visible Light

The effect of visible light on the skin has received very little attention, compared with UV radiation. The role of visible light, viewed as both physiologic and pathologic phenomena, and its effects on the skin are probably less important than the role of UV radiation. However, visible light sensitivity is an important phenomenon in diseases such as porphyria, solar urticaria, and other idiopathic photodermatoses, such as polymorphous light eruption. Patients who undergo photodynamic therapy treatments also become sensitive to visible light for a few days because of the accompanying topical medications, such as aminolevulinic acid and methylaminolevulinate, or for a few weeks due to systemic agents like porfimer sodium. A recent study by Mahmoud, et al. suggested that visible light exposure can increase pigmentation in patients with skin phototype IV to VI.^[8] Protection against visible light might be important for darker skinned patients who have pigmentary disorders such as post-inflammatory hyperpigmentation and melasma. Further research on the effects of visible light is definitely needed.

Organic sunscreen agents usually offer no protection against visible light, as their absorption spectrum is limited to UVB and UVA wavebands. Inorganic sunscreen agents, such as iron oxide, titanium dioxide, and zinc oxide can offer some visible light protection. However, the spectral protection of these agents varies according to their particle size. Larger particles of titanium dioxide and zinc oxide can protect in the visible range. Earlier formulations containing physical blocking agents tended to leave a white/pasty film on the skin, but with the advent of smaller-sized particles, modern physical sunscreens have made improvements in their effect on cosmetic appearance. Iron oxide is another physical UV blocking agent; however, it has the unique advantage of being closer to the natural skin color of phototype II and III individuals. The difference in visible light protection afforded by high SPF sunscreens with inorganic sunscreen agents was illustrated in a recent study that compared 2 inorganic sunscreens containing titanium dioxide, zinc oxide, and iron oxide for their ability to protect against blue light sensitivity induced by aminolevulinic acid application.^[9] The sunscreen containing 3.2% iron oxide (Avène Compact, Pierre Fabre Dermo-Cosmétique) offered a protection factor of 22:1 (i.e., the ratio of the lower blue light fluence that induced erythema on sunscreen protected skin to the lower blue light fluence that induced erythema on skin that was unprotected). Whereas the sunscreen with a lower concentration of 0.3% iron oxide offered only a protection factor of 2:1.

Cite this: Update on Sunscreens - Medscape - Jul 01, 2008.

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