Contact dermatitis is an inflammation of the skin that can be acute or chronic that manifests as eczematous dermatitis due to exposure to substances in the environment.

Allergic contact dermatitis is an immunologic cell-mediated skin reaction to exposure to antigenic substances.
The lesions initially appear on the cutaneous site of principal exposure then may spread to other more distant sites due to contact or autosensitization. Lesions are typically asymmetrical and unilateral.
Specific signs and symptoms will depend on the duration, location, degree of sensitivity and concentration of allergens. The patch test shows reaction to allergen.
Irritant contact dermatitis is a non-immunologic skin reaction to skin irritants.
It is often localized to areas of thin skin eg eyelids, intertriginous areas.


Allergic Contact Dermatitis

  • An immunologic cell-mediated skin reaction to exposure of antigenic substances; patch test positive

Irritant Contact Dermatitis

  • A nonimmunologic skin reaction to skin irritants; patch test negative

Differentiating between Allergic Contact Dermatitis & Irritant Contact Dermatitis:

  Allergic Contact Dermatitis Irritant Contact Dermatitis
Risk group Genetically predisposed Everyone
Mechanism of response Immunological response: Delayed hypersensitivity reactions Non-immunologic: Physical & chemical alteration of the skin epidermis
Nature of exposure Can be very low conc of low molecular wt hapten (eg metals, formalin, epoxy) after one or many exposures Normally high conc of organic solvent or soaps, etc after few to many exposures
Onset Usually hr to days Usually min to hr
Distribution May correspond exactly to contactant (eg elastic waist band, wristband) Indistinct borders
Diagnostic Test Based on patch test or usage test Based on trial of avoidance or negative patch test
Management Complete avoidance Protection & reduced incidence of exposure


Determine trigger factors based on:

  • Medical history
  • Physical exam
  • Questioning on the relationship between skin condition & include:
    • Date of onset
    • Occupation
    • Skin care products
  • Patch testing
    • Recommended in cases where symptoms persist despite avoidance of trigger factors & topical therapy
    • Not recommended as a diagnostic test for ICD
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