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- A cutaneous reaction to contact with an external substance
- Different mechanisms result in similar skin manifestation (1)
- Primary irritant dermatitis (ID) results from direct damage to the stratum corneum by chemicals or physical agents occurring faster than the skin is able to repair itself, leading to an inflammatory nonimmunologic cutaneous reaction. Prior sensitization is not required (2).
- Allergic contact dermatitis (ACD) affects only individuals previously sensitized to a substance. It represents a delayed hypersensitivity reaction, requiring several hours for the cascade of cellular immunity to be completed to manifest itself (2).
- System(s) affected: skin/exocrine
- Synonym(s): dermatitis venenata
Occupational contact dermatitis: 20.5/100,000 workers/year in one Australian study
- Contact dermatitis represents >90% of all occupational skin disorders.
- Predominant sex: male = female
- Variations due to differences in exposure to offending agents, as well as normal cutaneous variations between males and females (eccrine and sebaceous gland function and hair distribution)
Increased incidence of ID secondary to skin dryness
Increased incidence of positive patch testing due to better delayed hypersensitivity reactions (3)
Etiology and Pathophysiology
Hypersensitivity reaction to a substance generating cellular immunity response (4)
- Urushiol (allergen): poison ivy, poison oak, poison sumac
- Primary contact: plant (roots/stems/leaves)
- Secondary contact: clothes/fingernails (not blister fluid)
- Nickel: jewelry, zippers, hooks, and watches (5)
- Potassium dichromate: tanning agent in leather
- Paraphenylenediamine: hair dyes, fur dyes, and industrial chemicals
- Turpentine: cleaning agents, polishes, and waxes
- Soaps and detergents
- Topical medicines
- Neomycin: topical antibiotics
- Thimerosal (Merthiolate): preservative in topical medications
- Anesthetics: benzocaine
- Parabens: preservative in topical medications
- Formalin: cosmetics, shampoos, and nail enamel
Increased frequency of ACD in families with allergies
- Avoid causative agents.
- Use of protective gloves (with cotton lining) may be helpful.