Allergic Contact Dermatitis (ACD)

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

Irritant Contact Dermatitis (ICD)

• A non-immunologic skin reaction to skin irritants; patch test negative

 

	Allergic Contact Dermatitis (ACD)	Irritant Contact Dermatitis (ICD)
Risk group	Genetically predisposed	Everyone
Mechanism of response	Immunologic response: Delayed hypersensitivity reactions	Non-immunologic: Physical & chemical alteration of the skin epidermis
Nature of exposure	Can be very low concentration of low molecular weight hapten or allergen (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); may also be disseminated due to autosensitization	Distinct borders in acute ICD Indistinct borders in chronic ICD
Clinical manifestation	Usually in subacute & chronic phase	Usually in acute phase
Diagnostic test	Based on positive patch test or usage test	Based on trial of avoidance or negative patch test
Management	Complete avoidance of allergens nonpharmacologic & pharmacologic therapy	Protection & reduced incidence of exposure

Determine trigger factors based on:

• Medical history
  
  • Usually identifies the sensitizing agent or allergens in only 10-20% of cases
• Questioning the relationship between skin condition &:
  • Date of onset
  • Exposure to diapers, hygiene products, personal skin care products, sunscreens, clothing or fabrics w/ dyes, medications, pets, school supplies, sports uniform

Patch Test

• The gold standard for diagnosing allergic contact dermatitis (ACD)
• Result reading should be done 48 hours after application
• Allot another 30 minutes after application for erythema to settle after removing the tape/chamber
• Second reading must be done 3-7 days after initial patch application
• Results should be correlated w/ patient’s medical history
• Should only be done to children <6 years old w/ high degree of clinical suspicion for specific allergens
• Recommended in cases where symptoms persist despite avoidance of trigger factors & topical therapy
• Not recommended as a diagnostic test for irritant contact dermatitis (ICD)
• Avoid when allergic contact dermatitis (ACD) is active, flaring & covers >25% of body surface area (BSA)