The sun has many effects on the skin including sunburn, photoageing and tanning. The various responses to sun exposure depend on skin type and the ultraviolet light wavelength (see Chapters 39 and 40). The understanding of normal skin response to ultraviolet light is essential if abnormal responses are to be recognised. Fitzpatrick skin phototyping is most commonly used, from skin type 1 to skin type 6, based on assessing burning and tanning (see Chapter 39).

Sunburn Reaction

The acute skin response to ultraviolet B (UVB) exposure is termed sunburn reaction and this is an acute inflammatory response.

Sunburn presents with painful erythema on the sites of skin exposure to excess UVB. Onset of sunburn can be delayed for 4–6 hours after sun exposure and can peak at 16–24 hours. It typically fades over 2–3 days and can be followed by severe peeling of the skin and tanning.

Sunburn is mediated by an acute inflammatory response that causes damage of the epidermal cells via cytokines and up-regulation of inflammatory adhesion molecule expression.

Photoageing

Photoageing or chronic sun damage is brought about by a gradual change in the skin structure and function following long-term recurrent exposure to sunlight or artificial ultraviolet radiation (UVR) sources. This is due to cumulative DNA damage from recurrent acute DNA injury and from the effects of chronic inflammation. Background intrinsic genetic ageing changes can also occur. The epidermis and dermis are affected mainly by UVB but the dermis is also affected significantly by UVA which can penetrate more deeply.

Clinical signs include cutaneous fine and coarse wrinkling, coarseness, dryness, telangiectasia with pigmentation, increased laxity with loss of skin elasticity and comedones (Table 38.1; Figure 38.1).

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