PHOTOSENSITIVITY: IMPORTANT REACTIONS TO LIGHT
The term photosensitivity describes an abnormal response to light, usually referring to ultraviolet radiation (UVR). The two broad types of acute photosensitivity include the following:
A sunburn type response with the development of morphologic skin changes simulating a normal sunburn—erythema, edema, vesicles, and bullae—as seen in porphyria cutanea tarda and phytophotodermatitis.
A rash response to light exposure with development of varied morphologic expressions—macules, papules, plaques, eczematous dermatitis, urticaria—as seen in polymorphous light eruption (PMLE), solar urticaria, and eczematous drug reactions 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 obscured when the eyes are open normally), the skin on the upper lip and under the chin (submental area), a triangle behind the ears, the skin under a watchband, the area covered by a bathing suit, and the skin in body creases on the back and sides of the neck or abdomen.
ACUTE SUN DAMAGE (SUNBURN)
A sunburn is an acute, delayed, and transient erythema of the skin following exposure to UVR emitted from sunlight or artificial sources. Sunburn is characterized by erythema and, if severe, by vesicles and bullae, edema, tenderness, and pain.
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.
AGE All ages. Infants have an increased susceptibility.
PHOTOTYPES Most frequently seen in skin phototypes (SPT) I, II, and III (Table 16-1).
TABLE 16-1Fitzpatrick Classification of Skin Phototypes |Favorite Table|Download (.pdf) TABLE 16-1 Fitzpatrick Classification of Skin Phototypes
|Skin Phototype ||Reactivity to UVR ||Phenotype Examples |
|I ||Almost always sunburns, never tans ||White skin, blond hair, blue or brown eyes, freckles |
|II ||Usually sunburns, tans with difficulty ||White skin; red, blond, or brown hair, blue, hazel or brown eyes |
|III ||Sometimes sunburns, can tan gradually ||White skin, any color hair, any color eyes |
|IV ||Occasional sunburns, tans easily ||White or brown skin, dark hair, dark eyes |
|V ||Rarely sunburns, tans well ||Brown skin, dark hair, dark eyes |
|VI ||Almost never sunburns, tans well ||Dark brown or black skin, dark hair, dark eyes |
RACE Caucasian > Asian, American Indian > Black. Individuals with light skin, blue eyes, and blond/red hair are at greatest risk of sunburn.
ETIOLOGY Overexposure to UVB (290–320 nm) leads to erythema ...