Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 32-year-old woman is evaluated at a well-patient visit. Both her parents have a history of nonmelanoma skin cancer within the past year, and she is seeking counseling regarding skin cancer prevention. She has a history of remote sunburns and had previously tanned as a teenager. She requests advice on how to approach sun protection to limit both future skin cancer risk as well as to prevent wrinkles and cosmetic photodamage.

The patient has no other significant medical history and takes no medications.

On physical examination, vital signs are normal. She has mild scattered wrinkling, scattered solar lentigines, and an average number of benign-appearing nevi.

Which of the following is the most appropriate advice for this patient?

A: Maintain a baseline tan
B: Sunscreen with sun protection factor (SPF) 2 to 14
C: Sunscreen with SPF 15 or greater
D: Sunscreen with SPF 15 or greater plus UVA protection

MKSAP Answer and Critique

The correct answer is D: Sunscreen with SPF 15 or greater plus UVA protection.

This patient should use sunscreen with SPF 15 or greater plus UVA protection. Ultraviolet light is divided into categories based on wavelength: UVA (long wavelength) is the most deeply penetrating and can cause photoaging, tanning, and skin cancer, and UVB (shorter wavelength) penetrates less deeply but can cause both sunburns and skin cancer. The sun protection factor (SPF) measures the ability of a sunscreen to block UVB radiation and produce skin erythema determined under laboratory conditions. The SPF refers to the ratio of the dose of solar radiation needed to cause erythema on sunscreen-protected skin to the dose needed to cause erythema on unprotected skin, indicating the degree of protection. However, the relationship between SPF and degree of protection is not linear, such that an SPF of 30 is not twice as protective as an SPF of 15. SPF of 15 or more is required for adequate UVB protection; sunscreens with values lower than this can only be labeled to help decrease the risk of sunburn. To be considered “broad spectrum” sunscreens, the FDA mandates that products also provide protection against UVA.

Only sunscreens that have SPF 15 or higher and broad spectrum protection are known to reduce the risk of both skin cancer and signs of photoaging. Additionally, sunscreens may not be labeled as “waterproof” or “sweatproof” because they have not been proved to be effective for more than 2 hours, at which point they should be reapplied.

Although tanning is a natural defense mechanism in response to chronic sun exposure, it requires exposure to ultraviolet light, which increases the risk of photoaging and both melanoma and nonmelanoma skin cancers. Additionally, some patients are unable to tan and may simply burn with ultraviolet light exposure. Therefore, tanning should be discouraged.

Although randomized controlled data are lacking and there is no consensus U.S. Preventive Services Task Force guideline, mathematical modeling and small-scale studies note benefits in populations in which patients perform skin self-examinations. All patients at risk for skin cancer may benefit from performing monthly skin self-examinations, as many suspicious lesions, including melanomas, are detected initially by attentive patients. Although the sensitivity of skin self-examination is low, it has fair specificity, and patients who engage in skin self-examinations often detect skin cancers at an earlier stage when they are easier to treat and cure.

Key Point

• Only sunscreens that have SPF 15 or higher and broad spectrum protection are known to reduce the risk of both skin cancer and signs of photoaging.

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