Contact dermatitis is an inflammatory disorder of the skin resulting from exposure to irritant foreign substances. It can be classified into irritant contact dermatitis (ICD) and allergen contact dermatitis (ICD). In some cases, the irritants or allergens need to be activated by sunlight before causing any adverse effects and this is referred to as phototoxic dermatitis.


ICD accounts for 80% of contact dermatitis after exposure to irritant substances occur and this can be after a single or after repeated exposures. ICD can be catergorised depending on the irritant; chemical (solvents: petroleum based, daily household items such detergents, soap or perfumes, alcohol hand wash), physical (low humidity in air-conditioned room, temperature) or mechanical (friction and abrasive agents).


ICD is especially common in occupations that involve repeated hand washing (healthcare workers) or repeated exposure of the skin to water (cleaners), food materials, and other irritants (hairdressers). Interestingly, women are twice more likely to be affected than men.


Exposure to irritant or allergic substances can lead to disruption of the normal epithelial barrier. The pathogenesis of ICD involves epidermal cells, dermal fibroblasts, endothelial cells, and various leukocytes interacting with each other under the control of a network of cytokines and lipid mediators. Dermatitis manifests with erythema, oedema and scaling. Pruritus can be mild to severe, and pain accompanies erosions and fissures. This may also be complicated by secondary bacterial colonisation and infection.


In contrast, ACD occurs when substance induce a delayed (Type IV) hypersensitivity reaction resulting in inflammation. Langerhan cells (epidermal antigen presenting cells) engulf allergen compounds and present them to na´ve T-lymphocytes in the regional lymph nodes, which later release sensitised lymphocytes into the systemic circulation. Upon re-exposure, sensitised lymphocytes release cytokines at areas of exposure leading to inflammation. Patients often present with itchy papular erythmatous rash with indistinct margins. Potential allergens include latex, jewelleries and medications. ACD was first described in 1895 by Jadassohn, who also developed patch test for allergic testing.


The main treatment is avoidance of causal agents. Treatment consist of symptomatic treatment for pruritus, use of barrier cream (ceramide and dimethicone containing cream are helpful), antibiotic if infected and use of topical steroid can be use with caution if there is superimposed eczematous features.


Images contributed by Dr Maizatul and Dr Chong Vui Heng, Department of Internal Medicine, RIPAS Hospital, Brunei Darussalam.

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