Solar Radiation and Photoprotection

Published on 14/03/2015 by admin

Filed under Emergency Medicine

Last modified 14/03/2015

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8

Solar Radiation and Photoprotection

Erythemogenic doses of ultraviolet (UV) energy are defined as multiples of the minimal erythema dose (MED)—the lowest dose to elicit perceptible erythema. In a day’s time, a person can receive 15 MEDs of ultraviolet B (UVB) but only 2 to 4 MEDs of ultraviolet A (UVA). So, although humans are exposed to 10-fold to 100-fold more UVA than UVB, more than 90% of sunlight-induced erythema is attributable to UVB. However, UVA exposure contributes significantly to development of skin cancer. Almost all ultraviolet C (UVC) is absorbed by the earth’s ozone layer.

Acute Sunburn

Sunburn represents a local cutaneous inflammatory and vascular-mediated reaction. UVB erythema has its onset 2 to 6 hours after exposure, peaks at 12 to 36 hours, and fades over 72 to 120 hours. UVA erythema has its onset within 4 to 6 hours, peaks in 8 to 12 hours, and fades in 24 to 48 hours.

Treatment (Box 8-1)

Sunburn is self-limited, and its treatment is largely symptomatic.

1. Cool-water soaks or compresses may provide immediate relief. Moisturizers are sometimes helpful.

2. Topical anesthetics are sometimes useful. It is generally preferable to use nonsensitizing preparations containing menthol, camphor, and pramoxine rather than potentially sensitizing preparations containing benzocaine and diphenhydramine. Refrigerating topical anesthetics before application provides added relief.

3. Anecdotal remedies (controlled studies are lacking) include aloe, baking soda, and oatmeal (Aveeno).

4. Topical steroids (e.g., triamcinolone 0.1% cream applied bid when erythema first appears) may blanch reddened skin but should not be used on blistered skin. The combined use of topical steroids and oral nonsteroidal antiinflammatory drugs (NSAIDs) slightly decreases erythema during the first 24 hours if these drugs are administered before exposure or shortly after exposure, before sunburn becomes clinically apparent.

5. Systemic steroids (e.g., 3- to 5-days of prednisone) have anecdotal support but are not supported by any clinical trial.

6. Oral NSAIDs, including aspirin, provide analgesia and may reduce sunburn erythema.