Introduction
Contact Dermatitis_Disease Background 1
Contact dermatitis is any skin disorder brought about by contact with an exogenous substance that triggers an allergic and/or irritant response.
Epidemiology
Irritant contact dermatitis (ICD) accounts for approximately 80% of all contact dermatitis cases, while allergic contact dermatitis (ACD) comprises the remaining 20%. Data from the National Health and Nutrition Examination Survey (NHANES) estimates the overall prevalence of contact dermatitis in the United States at 1.4%, which closely aligns with a Dutch study that reported a 1.2% prevalence rate specifically for ACD. Allergic contact dermatitis accounts for up to 20% of all dermatitis cases in children. Irritant contact dermatitis commonly affects females more than males between ages 20-59 years old.
Pathophysiology
Allergic contact dermatitis is a type IV, T-cell–mediated, delayed hypersensitivity reaction initiated when a hapten penetrates the epidermal barrier that is accelerated by skin barrier disruption. The response progresses through a 10- to 14-day sensitization phase upon initial exposure, followed by an elicitation phase during subsequent exposures where antigen-specific T-cells are rapidly recruited to the site.
Irritant contact dermatitis is a non-immunologic inflammatory reaction that develops without prior sensitization, triggered directly by exposure to physical, chemical, or mechanical irritants. Pathophysiological changes in irritant contact dermatitis that may occur are disruption to the skin barrier, epidermal cellular changes, keratinocyte damage, and release of cytokines into the circulation.
Risk Factors
Common Trigger Factors
Allergic contact dermatitis is primarily triggered by medications, certain plants (eg Anacardiaceae [eg Toxicodendron/poison ivy, cashew nut tree, Indian marking nut tree, mango tree], Compositae or Asteraceae [eg ragweed, goldenrod, sunflowers, chamomile, chrysanthemums], Alliaceae [eg garlic, onion], Myrtaceae [eg tea tree]), metals, foods, fragrances, stabilizers in skin products, or preservatives, etc.
Irritant contact dermatitis is typically caused by strong alkaline soaps, organic solvents, acid, chlorinated or bleach-type ingredients, inhalants, airborne chemicals, etc. The location of inflammation may suggest trigger factors; for example, for the scalp and ears, the possible trigger factors are shampoo, hair dyes, topical medication, spectacles, metal earrings, etc.
Allergic Contact Dermatitis and Irritant Contact Dermatitis Related to Occupational Exposure
Exposure to cement, epoxy, glues, paint, and solvents may trigger allergic contact dermatitis. Irritant contact dermatitis is often seen in occupations involving food, salons or barbers, healthcare, and household cleaners. Fuels, lubricants, and cement may trigger irritant contact dermatitis.
Classification
Contact Dermatitis_Disease Background 2
Allergic Contact Dermatitis (ACD)
Allergic contact dermatitis is an immunologic cell-mediated skin reaction to exposure to antigenic substances. This can be suspected in patients with both generalized and anatomically localized skin eruptions (eg hands, face, eyelids) that have contact with exogenous substances. Diagnosis is made when the patch test is positive.
Irritant Contact Dermatitis (ICD)
Irritant contact dermatitis is a non-immunologic skin reaction to skin irritants; it is a patch test-negative or irritant reaction of different types. This results from innate immunity activation without prior sensitization and makes up about 80% of occupational contact dermatitis. In some situations, there is a simultaneous exposure to both an irritant and a contact allergen or two contact allergens that can reduce the clinical threshold concentration to elicit a response to a given allergen.
Difference between Allergic Contact Dermatitis and 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 and chemical alteration of the skin epidermis |
| Nature of exposure | Can be very low concentration of low molecular weight 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 and reduced incidence of exposure |