Irritant contact dermatitis

Overview

•ICD = direct physicochemical damage to the stratum corneum - no prior sensitisation required, reaction can occur on first exposure

•Non-immunological (contrast with allergic contact dermatitis - ACD - which is a Type IV delayed hypersensitivity, T-cell mediated, occurs 48-72 hours after exposure)

•Most common form of contact dermatitis; up to 80% of contact dermatitis cases are irritant in nature

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ACD (e.g. nickel watch rash) = Type IV hypersensitivity. ICD (e.g. detergent hands) = non-immunological direct irritation. Exam questions distinguish these two mechanisms.

Presentation

•Rash strictly confined to area of skin contact with the irritant (key distinguisher from ACD, which can spread beyond contact area)

•Chronic ICD (repeated low-level exposure): erythema, scaling, dryness, fissuring - especially dorsal hands and finger webs

•Acute ICD (single high-concentration exposure): vesicles, weeping, burning and stinging

•Symptoms improve away from the workplace - classic occupational history feature

•Pruritus vulvae - condom (latex) use is a common cause of vulval ICD; presents with redness and itch, no discharge

Investigations

•Primarily a clinical diagnosis - history of irritant exposure, rash confined to contact site, improvement away from irritant

•Patch testing - standard allergen series applied to back, read at 48 hours and again at 96-168 hours; used to identify allergens in suspected ACD and to exclude ACD; NOT diagnostic for ICD

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Patch testing is the investigation of choice for suspected ACD - not ICD. It is the correct answer when the question asks how to investigate a suspected contact allergen (e.g. occupational rash that may be allergic).

Differential diagnosis

Key differentials for hand/palmar vesicular rash

Feature	ICD	Pompholyx eczema	ACD
Distribution	Confined to contact site	Palms and soles	Contact site, may spread beyond
Trigger	Direct irritant (detergent, latex, friction)	Heat, sweating, humidity	Allergen (nickel, fragrances)
Mechanism	Non-immunological	Non-immunological	Type IV hypersensitivity
Vesicles	Acute only	Prominent - deep-seated	Can occur
Feet affected?	No - contact site only	Yes - plantar surface	Only if allergen contacts feet

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Pompholyx: vesicular rash on palms AND soles, triggered by sweating/heat/humidity - not confined to a contact area. ICD: rash only where irritant touched the skin.

Management

🥇 First-line

•avoidance of causative irritant - improvement may take 8-12 weeks after complete avoidance

•emollients and soap substitutes used liberally - restores barrier function; use instead of soap for all handwashing

•Protective measures if avoidance impossible - waterproof gloves during wet work, cotton liner gloves to reduce sweat maceration

🥈 Second-line

•topical corticosteroids - mild potency (e.g. hydrocortisone 1%) for facial/genital involvement; moderate to potent for hand dermatitis; applied once or twice daily during flares

•oral antihistamines - for symptomatic itch relief; sedating antihistamines may help at night

•Refer to dermatology if severe, chronic, recurrent, failing primary care management, or diagnosis unclear

•Occupational context: workplace modifications, occupational health assessment; employers have legal duty under COSHH regulations

Common irritants and triggers

Common irritants

Detergents and cleaning products

Frequent handwashing / wet work

Latex condoms

Industrial chemicals (acids, alkalis)

Friction

Water (prolonged contact)