Photodermatitis

Description

• Light-induced eruptions seen in a pattern of photodistribution
  • Phototoxic reactions: result of an acute toxic effect on skin of ultraviolet (UV) light alone (sunburn) or together with a photosensitizing substance (nonallergic) (1)
  • Photoallergic eruptions: a form of allergic dermatitis resulting from combined effects of a photosensitizing substance (drugs or chemical) plus UV light (immunologic/delayed hypersensitivity)
  • Polymorphous light eruption (PLE): chronic, intermittent, light-induced eruption with erythematous papules, urticaria, or vesicles on areas exposed to sunlight
• System(s) affected: skin/exocrine
• Synonym(s): sun poisoning; sun allergy

Epidemiology

Incidence

• PLE usually occurs after the first intense exposure to the sun in the spring or summer.
• Predominant age: all ages
• Predominant sex: male = female

Prevalence
May be as high as 20% in some areas

Etiology and Pathophysiology

• Sunlight
• Phenothiazines
• Diuretics
• Tetracyclines, sulfonamides
• Oral contraceptives
• Topicals: psoralens, retinoids coal tars, photoactive dyes (eosin, acridine orange)
• 5-Fluorouracil
• Quinine
• Sunscreens containing para-aminobenzoic acid (PABA)
• In the United States, ~115 chemical agents used topically are known to cause photodermatitis.

Genetics
Predisposition occurs in inbred populations (e.g., Pima Indians).

Risk Factors

• Job-related exposure to sunlight
• Light- and fair-colored skin

General Prevention

• Sunlight avoidance/protective clothing
• Identification and avoidance of causative drugs (see “Etiology and Pathophysiology”)
• Sunscreens: Apply before exposure:
  • Zinc oxide: opaque, cosmetically less acceptable; some preparations are available that when applied dry clear
  • Chemical: Use sun protective factor (SPF) >30 for maximum protection; substantively resistant to sweat and swimming; cosmetically more acceptable (2)
• Avoid direct sun exposure.
• Use appropriate clothing and hats to avoid sunlight exposure (3).

Commonly Associated Conditions

• Sunlight aggravation of systemic lupus erythematosus (SLE)
• Persistent light reactivity
• Actinic reticuloid