UVB penetrates the epidermis and superficial dermis, stimulating the production and release of prostag-landins, leukotrienes, histamine, interleukin 1 (IL-1) and tumour necrosis factor α (TNF-α), which cause pain and redness.
Skin exposed to too much UVB smarts and becomes red several hours later. Severe sunburn is painful and may blister. The redness is maximal after 1 day and then settles over the next 2 or 3 days, leaving sheet-like desquamation (Fig. 16.3), diffuse pigmentation (a ‘tan’) and, sometimes, discrete lentigines.
Phototoxic reactions caused by drugs are like an exag-gerated sunburn.
None are required.
The treatment is symptomatic. Baths may be cooling and oily shake lotions (e.g. oily calamine lotion), oil-in-water lotions or creams comforting. Potent topical corticosteroids (Formulary 1) help if used early and briefly. Oral aspirin (a prostaglandin synthesis inhibitor) relieves the pain. Sprays containing benzo-caine also relieve pain, but occasionally sensitize.