Prevention

Given the strong etiologic link between UVR and SC, reducing exposure to sunlight or other forms of UVR is the single most important measure in preventing SC.⁶⁰ General protection guidelines published by the American Cancer Society include avoiding sun exposure when UV rays are strongest (between 10 AM and 4 PM); wearing protective clothing; wearing a hat that shades the neck, face and ears; wearing sunglasses that block UV rays; and properly (liberally) using a broad spectrum sunscreen with a sun protection factor (SPF) of 30 or higher.⁶¹

The SPF of a sunscreen product is determined using a calibrated artificial UV radiation source to induce minimal erythema on skin protected by the application of 2 mg/cm² of the test sunscreen.⁶² SPF is the ratio of UV radiation dose required to induce minimal erythema on protected skin versus the dose required to induce the same degree of erythema on unprotected skin.^62,63 It is of note that UV-B radiation is 1,000 - 10,000 times more carcinogenic than UV-A radiation.^64,65

Sunscreens are divided into two types: inorganic and organic and there are currently 17 agents approved for use in the United States.⁷ Inorganic sunscreens contain zinc or titanium dioxide and act to physically block, reflect, or scatter UV radiation.^7,66 Organic agents have variable absorptive spectra and sunscreen manufacturers typically combine several agents to produce a broad spectrum product capable of blocking both UV-A and UV-B.^7,64,67 Table 3 lists selected FDA-accepted sunscreen agents, their allowable concentrations, and their UVR spectrum.

For the prevention of SC, the product chosen should be formulated for use on the lip and provide broad-spectrum protection against both UV-B and UV-A radiation.^7,66,67 Table 4 lists some commercially available broad spectrum lip sunscreens/sunblocks. As product lines and formulations are subject to change, clinicians and consumers should always check the product label. If a lip balm is not available, a broad-spectrum liquid or gel sunscreen applied to the lips may prove effective.⁶⁷

Regardless of the product chosen, sunscreens should be applied liberally 15-30 minutes prior to exposure to UVR.^61,66 They should be reapplied liberally after any vigorous activity that may wash or rub away the product.^61,68 Finally, and perhaps more importantly, the patient should be educated that the purpose of sunscreens is to provide protection against UV radiation when one needs to be outside, but that the ultimate goal of prevention is to reduce elective sun exposure.