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
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.
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
Phototypes Most frequently seen
in skin phototypes (SPT) I, II, and III (Table 16-1).
Table 16-1 Fitzpatrick
Classification of Skin Types ||Download (.pdf)
Table 16-1 Fitzpatrick
Classification of Skin Types
|Skin Type||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
|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 > 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.