Irritant contact dermatitis vs Allergic contact dermatitis
How to tell Irritant contact dermatitis and Allergic contact dermatitis apart when a board question makes them look alike.
Irritant is direct toxic barrier damage with burning; allergic is delayed type IV pruritic vesicular dermatitis after sensitization.
Side by side
Irritant contact dermatitis causes burning, stinging, dryness, and inflammation limited to direct chemical or friction exposure, often after repeated wet work or solvents.
Allergic contact dermatitis is a type IV hypersensitivity reaction with pruritic vesicles or eczematous rash after sensitization, often spreading beyond contact area.
Direct barrier injury damages keratinocytes without requiring immune sensitization.
Hapten-specific T cells mediate delayed hypersensitivity after prior sensitization.
Immediate exposure-related burning and sharply exposed-area dermatitis support irritant contact dermatitis.
Delayed intensely itchy vesicular rash and positive patch testing support allergic contact dermatitis.
The trap
Both follow contact exposure, so timing, itch versus burn, and need for prior sensitization separate them.
The repair move
For contact dermatitis, decide direct irritation versus delayed allergic sensitization.
Try a free question
CoreA 28-year-old healthcare worker has 4 months of dry, scaly, painful skin on both hands after starting frequent hand hygiene with alcohol-based sanitizer and soap. The dermatitis appeared within days to weeks of starting and worsens with each subsequent exposure. Patch testing is negative. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Irritant contact dermatitis. Irritant contact dermatitis is direct cytotoxic damage to skin barrier from chemical exposure (soaps, detergents, alcohols, acids); onset can be immediate, lacks immune memory, and patch testing is negative; treatment is barrier protection and avoidance.
Why the other choices are tempting
- B. Allergic contact dermatitis is type IV delayed hypersensitivity with positive patch testing.
- C. Atopic dermatitis has atopic history and flexural distribution.
- D. Dyshidrotic eczema has tense vesicles on the lateral fingers and palms.
- E. Psoriasis has well-demarcated silvery-scaled plaques and characteristic histology.
Flashcards
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What immune type is allergic contact dermatitis?
Allergic contact dermatitis is type IV hypersensitivity.
What symptom favors irritant dermatitis?
Burning or stinging favors irritant contact dermatitis.
Quick answers
What is the fastest way to tell Irritant contact dermatitis from Allergic contact dermatitis?
Irritant is direct toxic barrier damage with burning; allergic is delayed type IV pruritic vesicular dermatitis after sensitization.
What is the key clue for Irritant contact dermatitis?
Irritant contact dermatitis causes burning, stinging, dryness, and inflammation limited to direct chemical or friction exposure, often after repeated wet work or solvents.
What is the key clue for Allergic contact dermatitis?
Allergic contact dermatitis is a type IV hypersensitivity reaction with pruritic vesicles or eczematous rash after sensitization, often spreading beyond contact area.
What is the common trap with Irritant contact dermatitis vs Allergic contact dermatitis?
Both follow contact exposure, so timing, itch versus burn, and need for prior sensitization separate them.