What are the signs and symptoms of allergic contact dermatitis?

Signs and Symptoms of Allergic Contact Dermatitis

Allergic contact dermatitis presents with erythema, vesiculation, and pruritus in the acute phase, while the chronic phase is characterized by dryness, lichenification, and fissuring at the site of allergen exposure. 1

Key Clinical Features

• Acute phase manifestations:

  • Erythema (redness) at the site of allergen contact 1
  • Vesiculation (small fluid-filled blisters) 1
  • Pruritus (itching) - often intense 2
  • Well-demarcated borders that correspond to the area of allergen contact 2
  • In severe cases, dramatic flares with bullae (larger blisters) may occur 2

• Chronic phase manifestations:

  • Dryness and scaling of affected skin 1
  • Lichenification (thickening of skin with accentuated skin markings) 1
  • Fissuring (painful cracks in the skin) 1
  • Persistent erythema 3

Distribution and Patterns

• The rash appears specifically at sites of allergen contact 4
• Common locations include hands, face, and areas exposed to jewelry, cosmetics, or occupational allergens 5
• The pattern and distribution often provide clues to the causative allergen 1
• Linear streaks may be seen with plant exposures (e.g., poison ivy) 5

Differentiating Allergic from Irritant Contact Dermatitis

Allergic and irritant contact dermatitis can be difficult to distinguish clinically, but some features may help differentiate them:

• Allergic contact dermatitis:

  • Requires prior sensitization to the allergen 1
  • Often spreads beyond the area of direct contact 3
  • May take 48-96 hours to develop after exposure in sensitized individuals 1
  • Generally has worse prognosis unless the allergen is identified and avoided 1

• Irritant contact dermatitis:

  • Does not involve immune sensitization 1
  • Usually confined to the area of direct contact with the irritant 1
  • Can occur on first exposure to strong irritants 1
  • Better prognosis if the irritant is removed 1

Diagnostic Challenges

• Clinical features alone are unreliable in distinguishing allergic contact from irritant and endogenous dermatitis, particularly with hand and facial dermatitis 6, 1
• Patch testing is the gold standard for confirming allergic contact dermatitis, with sensitivity and specificity between 70% and 80% 6
• Contact dermatitis can mimic various other skin conditions including atopic dermatitis, psoriasis, and infectious conditions 4

Common Allergens

• Metals (particularly nickel) 1
• Fragrances in cosmetics, soaps, and personal care products 1, 5
• Plants (poison ivy, oak, sumac) 5
• Preservatives in topical products 1
• Rubber accelerators 1
• Topical antibiotics 1
• Jewelry components 5
• Cosmetic ingredients 5

Clinical Course and Complications

• Without allergen identification and avoidance, allergic contact dermatitis tends to become chronic 1
• Secondary bacterial infection may occur, particularly with scratching 3
• Chronic cases may lead to significant quality of life impairment and occupational disability 3
• Systemic symptoms are rare but can include fever and malaise in severe widespread cases 7

Remember that patch testing is essential for confirming the diagnosis of allergic contact dermatitis and identifying the specific allergen(s) responsible, as clinical features alone are insufficient for definitive diagnosis 6, 1.