Description

• A cutaneous reaction to an external substance
• Each type has a different mechanism, whereas the clinical presentation is the same (1).
• Primary irritant dermatitis (ID) is a result of direct damage to the stratum corneum by chemicals or physical agents that occurs faster than the skin is able to repair itself, which results in an inflammatory nonimmunologic cutaneous reaction. Prior sensitization is not required (2). ID occurs immediately or within 48 hours of exposure.
• Allergic contact dermatitis (ACD) affects only individuals previously sensitized to a substance. It represents a delayed hypersensitivity reaction, requiring several hours or days for the cascade of cellular immunity to manifest itself (2).
• System(s) affected: skin/exocrine
• Synonym(s): dermatitis venenata

Epidemiology

Common

Incidence
Occupational contact dermatitis accounts for up to 70% of occupational skin disease occurrences and affects 20.5/100,000 workers per year in one Australian study.

Prevalence

• Florists, hairdressers, cooks, beauticians, health care workers, and metal-working machine operators have the highest incidence.
• 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)

Geriatric Considerations
Increased incidence of ID secondary to skin dryness

Pediatric Considerations
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

• Plants
  • Urushiol (allergen): poison ivy, poison oak, poison sumac
  • Primary contact: plant (roots/stems/leaves)
  • Secondary contact: clothes/fingernails (not blister fluid—the established eruption is not itself contagious or transmissible)
• Chemicals
  • Nickel: jewelry, zippers, hooks, and watches (4)
  • 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

Genetics
Increased frequency of ACD in families with allergies

Risk Factors

• Occupation
• Hobbies
• Travel
• Cosmetics
• Jewelry

General Prevention

• Avoid causative agents.
• Use of protective gloves (with cotton lining) may be helpful.