What causes unilateral allergic reactions of the eyelids, affecting either the top or bottom eyelid?

Causes of Unilateral Allergic Reactions of the Eyelids

Unilateral eyelid allergic reactions affecting only the upper or lower lid are most commonly caused by allergic contact dermatitis from direct exposure to allergens through hand transfer, cosmetics, nail lacquer, ophthalmic medications, or preservatives, rather than systemic allergic conjunctivitis which typically presents bilaterally. 1, 2

Primary Causes of Unilateral Eyelid Reactions

Allergic Contact Dermatitis (Most Common)

• Allergic contact dermatitis is the most frequently reported cause of eyelid dermatitis, representing a type IV delayed hypersensitivity reaction to external allergens 1, 2
• The unilateral and segmental (upper or lower lid only) presentation occurs because the allergen contacts only specific areas through:
  • Hand transfer patterns (touching one eye after handling allergens like nail lacquer, cosmetics, or workplace chemicals) 1
  • Direct application of cosmetics or ophthalmic medications to one lid 3, 2
  • Airborne allergens depositing asymmetrically (fragrances, hair products) 1

Common Allergen Sources

• Metals (nickel from eyelash curlers, tweezers, eyeglass frames) 1
• Fragrances (perfumes, scented cosmetics, hair products) 1, 2
• Preservatives (in cosmetics and ophthalmic medications, including phenylephrine hydrochloride) 1, 3
• Acrylates (false eyelash adhesives, nail products transferred by hand) 1
• Topical medications (ophthalic preparations, sympathomimetics) 1, 3
• Nail lacquer (transferred by rubbing or touching the eye) 1

Secondary Causes of Unilateral Presentation

Drug-Induced Angioedema

• Angioedema frequently presents as a unilateral reaction affecting upper and/or lower eyelids, often with associated bulbar conjunctival congestion 4
• Symptoms typically begin 1-2 hours after drug exposure and may persist for hours to days 4
• NSAIDs like loxoprofen sodium can cause unilateral eyelid angioedema 4

Infectious Causes Mimicking Allergy

• Molluscum contagiosum typically presents unilaterally with follicular conjunctivitis and can affect surrounding eyelid structures 5
• Herpes simplex virus usually presents unilaterally with eyelid involvement and conjunctival injection 5
• Varicella zoster can be unilateral with vesicular dermatomal rash affecting eyelids 5

Diagnostic Approach

Key Clinical Features to Identify

• Examine for asymmetric allergen exposure patterns: check which hand is dominant, nail lacquer use, cosmetic application habits 1
• Look for distinctive signs of contact dermatitis: erythema, pruritus, edema confined to areas of allergen contact 2
• Differentiate from infectious causes: absence of vesicles (HSV/VZV), umbilicated lesions (molluscum), or purulent discharge (bacterial) 5
• Assess for pure edematous swelling without other inflammatory signs, which may indicate angioedema rather than contact dermatitis 3

Diagnostic Testing

• Epicutaneous patch testing is the gold standard for diagnosing allergic contact dermatitis of the eyelids 1, 2
• Expanded patch testing panels should include metals, fragrances, preservatives, acrylates, and topical medications 1
• Consider oral challenge testing if drug-induced angioedema is suspected 4

Critical Pitfalls to Avoid

• Do not assume bilateral presentation is required for allergic etiology - contact dermatitis commonly presents unilaterally based on exposure patterns 1, 4
• Pure edematous swelling requires thorough evaluation to exclude orbital, lacrimal, or sinus pathology before attributing to allergy 3
• Distinguish between allergic contact dermatitis (type IV hypersensitivity) and immediate hypersensitivity reactions (angioedema, urticaria) as management differs 6, 4
• Examine surrounding skin and nails for additional clues to allergen source, as eyelid involvement may be secondary to hand transfer 1, 2

Management Principles

• Strict allergen avoidance is the cornerstone of treatment once the specific allergen is identified through patch testing 1, 2
• Patient counseling about hidden allergen sources (nail products, hair sprays, eyeglass frames) is essential for successful management 1
• Topical anti-inflammatory agents can provide long-term control of eyelid findings in allergic contact dermatitis 2
• Oral corticosteroids may be necessary for acute angioedema episodes 4