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Contact Dermatitis

Basics

  • Cutaneous reaction to external substance.
  • Two types:
  • Primary irritant dermatitis (ID): Nonimmunologic inflammatory reaction from direct skin damage; no prior sensitization needed; occurs immediately or within 48 hours.
  • Allergic contact dermatitis (ACD): Delayed hypersensitivity reaction; requires prior sensitization; develops over hours to days.
  • Synonym: dermatitis venenata.
  • Systems affected: skin/exocrine.

Epidemiology

  • Common occupational skin disease; up to 70% of occupational dermatoses.
  • Incidence ~20.5 per 100,000 workers/year in Australia.
  • High-risk occupations: florists, hairdressers, cooks, beauticians, health care workers, metal workers.
  • Equal male/female distribution; exposure and skin differences influence incidence.
  • Geriatric: increased irritant dermatitis due to skin dryness.
  • Pediatric: higher positive patch testing rates (better delayed hypersensitivity).

Etiology and Pathophysiology

  • Hypersensitivity reaction mediated by cellular immunity.
  • Common allergens and irritants:
  • Plants: Urushiol (poison ivy, poison oak, poison sumac).
  • Chemicals: Nickel (jewelry, zippers), potassium dichromate (leather tanning), paraphenylenediamine (hair dyes), turpentine, soaps/detergents.
  • Topical medications: Neomycin, thimerosal, benzocaine, parabens, formalin.
  • Genetics: increased ACD frequency in families with allergies.

Risk Factors

  • Occupational exposure.
  • Hobbies and travel.
  • Use of cosmetics and jewelry.

General Prevention

  • Avoid known causative agents.
  • Use protective gloves with cotton lining.

Diagnosis

History

  • Itchy rash.
  • Prior exposure to irritants or allergens.

Physical Exam

  • Acute: papules, vesicles, bullae with erythema; crusting and oozing; pruritus.
  • Chronic: erythematous base; lichenification; scaling; fissuring.
  • Distribution: thin skin areas (eyelids, genitalia), contact sites (e.g., nail polish), palmar/soles relatively resistant but common hand dermatitis.
  • Lesions: well-demarcated, sharp borders and angles, linear arrays.
  • Pathognomonic: papulovesicular rash in well-defined area.

Differential Diagnosis

  • Vesicular lesions: herpes simplex, bullous pemphigoid.
  • Photodistributed: phototoxic/allergic reactions.
  • Eyelid involvement: seborrheic dermatitis.
  • Eczematous conditions: atopic dermatitis, nummular eczema, lichen simplex chronicus, stasis dermatitis, xerosis.
  • ID reaction.

Diagnostic Tests

  • Patch testing to identify allergens; recent steroid use may alter results.
  • Histology: intercellular edema, bullae formation.

Treatment

General Measures

  • Identify and remove offending agent.
  • Avoidance and work modification.
  • Protective clothing.
  • Barrier creams (high-lipid moisturizers).
  • Topical soaks: cool water, Burow solution, saline, silver nitrate.
  • Lukewarm baths, oatmeal baths.
  • Emollients (petrolatum, Eucerin).

Medications

  • First Line:
  • Topical: zinc oxide, talc, menthol lotion, phenol.
  • Corticosteroids: high-potency (fluocinonide 0.05%) for short-term; then switch to lower potency; caution on face/folds.
  • Calamine lotion for symptom relief.
  • Topical antibiotics if secondary infection present.
  • Systemic:
  • Antihistamines (hydroxyzine, diphenhydramine, cetirizine) for pruritus.
  • Oral corticosteroids (prednisone taper 60-80 mg/day over 10-21 days) for moderate to severe or facial/genital involvement.
  • Antibiotics for secondary bacterial infection (dicloxacillin, amoxicillin-clavulanate, cephalexin, TMP-SMX for resistant strains).

Precautions

  • Antihistamines cause drowsiness.
  • Prolonged topical steroids may cause skin atrophy, striae, telangiectasia.
  • Oral steroids >5 days should be tapered.

Second Line

  • Other antibiotics based on cultures.
  • Pregnancy caution with medications.

Issues for Referral

  • Dermatology or allergy referral if refractory.

Complementary & Alternative Medicine

  • Supplement, not replacement, for conventional treatment.

Admission/Inpatient Considerations

  • Rarely needed.

Ongoing Care

  • Monitor for recurrence.
  • Patch testing after resolution.

Diet

  • No special diet.

Patient Education

  • Avoid irritants.
  • Clean secondary sources (nails, clothing).
  • Blister fluid is not contagious.

Prognosis

  • Self-limited and benign.
  • 55% have persistent dermatitis 2 years post diagnosis.
  • Poor prognosis if exposure persists or with atopy.

Complications

  • Autosensitization with generalized eruption.
  • Secondary bacterial infection.

ICD10 Codes:
- L25.9 Unspecified contact dermatitis
- L23.9 Allergic contact dermatitis, unspecified cause
- L25.5 Contact dermatitis due to plants (except food)

Clinical Pearls:
- Commonly affects hands and face.
- High-risk exposures in chemical-heavy occupations.
- Poison ivy/oak/sumac dermatitis needs 10-14 days steroid therapy to prevent rebound.
- Nickel is the most frequent allergen on patch testing worldwide.
- Treatment centers on allergen avoidance and temporary topical steroids.
- Rash follows nondermatomal geographic distribution consistent with exposure.