Section 16

The term photosensitivity describes an abnormal response to light, usually ultraviolet radiation (UVR). Following are the two broad types of acute photosensitivity:

1. A sunburn type response with the development of morphologic skin changes simulating a normal sunburn—erythema, edema, vesicles, and bullae—for example, porphyria cutanea tarda and phytophotodermatitis.

2. A rash response to light exposure with development of varied morphologic expressions—macules, papules, plaques, eczematous dermatitis, urticaria—for example, polymorphous light eruption, urticaria, and eczematous drug reaction to sulfonamides.

The skin response to light exposure is strictly limited to the areas that have been exposed, and sharp borders are usually noted.

It should be noted that sparing of certain skin areas may provide the clue to photosensitivity—the upper eyelids (which are closed, normally), the skin on the upper lip and under the chin (submental area), a triangle behind the ears, skin under a watchband, area covered by a bathing suit, or skin in body creases on the back and sides of the neck or the abdomen.

Acute Sun Damage (Sunburn)

A sunburn is an acute, delayed, and transient erythema of the skin following exposure to ultraviolet radiation (UVR) emitted from sunlight or artificial sources. Sunburn is characterized by erythema and, if severe, by vesicles and bullae, edema, tenderness, and pain.

Classification

UVR sunburns can be divided into UVB (290–320 nm) erythema, which develops in 12 to 24 hours and fades within 72 to 120 hours, and UVA (320–400 nm) erythema, which peaks between 4 and 16 hours and fades within 48 to 120 hours.

Epidemiology

Age All ages. Infants have an increased susceptibility.

Gender M = F.

Phototypes Most frequently seen in skin phototypes (SPT) I, II, and III (Table 16-1).

Table 16-1 Fitzpatrick Classification of Skin Types

Race Caucasian > brown > black.

Etiology Overexposure to UVB (290–320 nm) leads to erythema and edema. The skin reaction can be augmented by photosensitization drugs or chemicals (psoralens, sulfonamides, tetracyclines, doxycycline, etc). The intensity of UVR is augmented by reflective surfaces (snow, sand, water), altitude, and latitudes near the equator.

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