contact%20dermatitis
CONTACT DERMATITIS

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.

Diagnosis

Allergic Contact Dermatitis

  • An immunologic cell-mediated skin reaction to exposure of antigenic substances; patch test-positive
  • Can be suspected in patients w/ both generalized & anatomically localized skin eruptions (eg hands, face, eyelids) that had contact w/ exogenous substances

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 concentration of low molecular wt hapten (eg metals, formalin, epoxy) after one or many exposures Normally high concentration of organic solvent or soaps, etc after few to many exposures
Onset Usually hours to days Usually minutes to hours
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

History

Determine trigger factors based on:

  • Medical history
  • Physical exam
  • Questioning on the relationship between skin condition & include:
    • Date of onset
    • Occupation
    • Skin care products

Screening

Patch testing
  • Gold standard test in a patient wherein allergic contact dermatitis is suspected
  • Involves reproducing under patch tests of an allergic contact dermatitis in an individual sensitized to a particular antigen
  • Recommended in cases where symptoms persist despite avoidance of trigger factors & topical therapy
  • Sensitivity of this test is 70% & specificity is 80%
  • Not recommended as a diagnostic test for irritant contact dermatitis
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