Allergic contact dermatitis
See also in: Cellulitis DDx,External and Internal Eye,Anogenital,Hair and Scalp,Nail and Distal Digit,Oral Mucosal LesionAlerts and Notices
Synopsis
Contact dermatitis presents as either allergic or irritant in etiology. While irritant contact dermatitis represents the direct toxic effect of an offending agent on the skin, allergic contact dermatitis (ACD) represents a delayed-type (type IV) hypersensitivity reaction that occurs when allergens activate antigen-specific T cells in a sensitized individual. Consequently, whereas irritant contact dermatitis can occur after one exposure to the offending agent, ACD typically requires repeat exposures before an allergic response is noted. ACD can occur 24-48 hours after exposure to the offending agent.
Contact dermatitis can demonstrate well-demarcated borders, suggestive of an "outside job" or external contact. The most common contact allergens are urishiol (poison ivy, oak, or sumac), nickel, fragrance, cobalt (a metal; see also cobalt toxicity), chromates (leather products), neomycin, thimerosal (ophthalmic preparations and vaccines), adhesives, and oxybenzone (sunscreens). Formaldehyde-releasing preservatives in polypropylene surgical masks have been reported to cause ACD.
The distribution and geometry of lesions are important clues to diagnosis. It can also present as a systemic contact reaction with widespread lesions when the offending agent is ingested or present in an implanted device. ACD can occur in reaction to topical agents, ingested agents, implanted biomedical devices, and airborne materials.
American Contact Dermatitis Society Allergen of the Year:
- 2020 – Isobornyl acrylate, an acrylic monomer often used as an adhesive in medical devices. There have been multiple case reports of diabetes patients developing contact allergies to their insulin pumps. Acrylic nails are also a potential source. Clinician awareness is important because testing using routine panels does not identify isobornyl acrylate.
- 2021 – Acetophenone azine, thought to be formed in situ through reactions between ethyl vinyl acetate, which is present in foams used for cushioning in shin pads and footwear, and other additives. Reactions have been noted mostly in children and teens ("soccer shin" contact dermatitis).
Codes
ICD10CM:L23.9 – Allergic contact dermatitis, unspecified cause
SNOMEDCT:
40275004 – Contact dermatitis
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Diagnostic Pearls
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Differential Diagnosis & Pitfalls
- Atopic dermatitis
- Irritant contact dermatitis
- Nummular dermatitis (nummular eczema)
- Dyshidrotic dermatitis (dyshidrotic eczema)
- Insect bite reaction
- Stasis dermatitis
- Tinea corporis
- Psoriasis – Cases of ACD to topical nail agents mimicking psoriasis have been reported.
- Palmoplantar psoriasis
- Pityriasis rosea
- Photoallergic dermatitis – Can be distinguished from airborne ACD by the absence of dermatitis on the upper eyelid crease and on the central neck under the chin.
- Seborrheic dermatitis – The distribution of lesions is often a helpful clue in distinguishing this entity from atopic dermatitis.
- Lichen simplex chronicus
- Ichthyosis vulgaris
- Scabies
- Pityriasis rubra pilaris
- Secondary syphilis
- Glucagonoma syndrome
- Pellagra
- Cutaneous T-cell lymphoma / mycosis fungoides – If an adult patient has persistent "eczema" that is not adequately responding to therapy, this entity should be ruled out with skin biopsies.
- Cellulitis
- Tinea pedis
- Erysipelas
- Herpes simplex virus infection
- Impetigo
- Erythema multiforme
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Management Pearls
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Therapy
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Drug Reaction Data
Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.Subscription Required
References
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Last Reviewed:10/02/2017
Last Updated:06/30/2022
Last Updated:06/30/2022
Allergic contact dermatitis
See also in: Cellulitis DDx,External and Internal Eye,Anogenital,Hair and Scalp,Nail and Distal Digit,Oral Mucosal Lesion