Core Dermatology Diagnoses / CategoriesInflammatory

Contact dermatitis

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Publish date: Posted on
Last updated: March 18, 2021

Keywords #

allergic contact dermatitis
irritant contact dermatitis
patch testing

Diagnosis #

Contact dermatitis includes both allergic (ACD) and irritant contact dermatitis (ICD). ACD and ICD are both inflammatory skin conditions that result from direct skin contact with external substances that either exert a toxic effect on the skin (ICD) or activate the adaptive immune system (ACD).[1] Contact dermatitis can affect all areas of skin. The distribution of skin disease is the most important factor in identifying a relevant irritant or allergen. Patch testing is the gold standard in determining allergy to a specific chemical substance. There are thousands of potential irritants and allergens.

Key Concepts #
  • Allergic contact dermatitis may develop anywhere from 24 hours to a week after exposure to an allergen.
  • Common allergens include nickel, urushiol (poison ivy, oak, sumac), fragrance, methylisothiazolinone/methylchloroisothiazolinone, formaldehyde, and rubber chemicals.
  • Patch testing is a week-long process that involves testing of specific allergens.
  • Irritant contact dermatitis often develops after repetitive exposure to mild irritants or immediately following exposure to strong irritants.
  • Acute treatment includes topical or oral steroids during significant flares.
  • The best treatment is avoidance of allergens and irritants.
Epidemiology #

It is suspected that 20% of the population has a contact allergy. 80% of all contact dermatitis is ICD while 20% is ACD.1 10% of ACD and 37% of ICD is occupationally related. The most common allergens are nickel (17.5%), methylisothiazolinone (13.4%), fragrance mix I (11.3%), and formaldehyde (8.4%).[2] Development of contact dermatitis is influenced by exposure, occupation, age, and history of atopy.[1-2]

Clinical Features #
  • Irritant contact dermatitis ranges in appearance depending on the irritant and exposure pattern.
  • Acute ICD appears seconds to minutes after exposure as erythematous and edematous areas with the development of tender vesicles and bullae.
  • More commonly, chronic ICD from repeated exposures appears as lichenified, erythematous areas with scale and fissuring; there may be both pain and itching.
  • Both acute and chronic ICD are limited to the contact site but often have less distinct borders.[3]
  • The hands are commonly involved.
  • Allergic contact dermatitis is a delayed response that takes up to a week after initial exposure to develop. The rash typically arises within 24-96 hours on subsequent exposures.
  • Itching is the predominant symptom.
  • Erythema, vesicles and bullae are often pronounced in the acute phase but chronic ACD may appear similar to chronic ICD as lichenified and erythematous areas.[1]
  • Areas of involvement may be sharply-demarcated.[3]
  • The hands, face, or feet are commonly involved.
Differential Diagnoses #
Diagnostic Workup #

The diagnosis of ICD and ACD are often made clinically based on clinical suspicion, appearance, exposure history, and distribution pattern. Patch testing is the definitive way to identify allergies. Patch testing involves placing specific chemicals on the back, removing them and doing a preliminary read at 48 hours, and performing a final read at 5-7 days to examine for delayed reactions.[2] There are numerous panels used for patch testing, which are personalized to the individual. There is no specific test available to determine ICD.

Biopsy of acute ICD is characterized by necrosis of keratinocytes and mild spongiosis with a perivascular mononuclear infiltrate. Chronic ICD shows hyperkeratosis, parakeratosis, and acanthosis. Biopsy of acute ACD often shows epidermal spongiosis with an eosinophilic infiltrate but can have a variety of pathology presentations. Chronic lesions show epidermal acanthosis with hyperkeratosis with minimal spongiosis and inflammation. It is difficult to distinguish ACD from ICD and other forms of dermatitis by biopsy.[4]

Treatment #

The initial treatment of contact dermatitis involves topical steroids or in severe/refractory cases, oral steroids. Avoidance of allergens and irritants is imperative; counseling on numerous cross-reactors and reading of ingredient labels is necessary. The Contact Allergen Management Program (CAMP) is a useful tool that provides patients a personalized “safe” list of personal care products free of their allergens.[5] Depending on the site of involvement, barrier protection may be a useful tool (particularly in occupational settings). For hand dermatitis, vinyl gloves are the least allergenic type of protection.

video source: https://www.chemotechnique.se/patch-testing/patch-test-instructions/

References #
  1. Peiser M, Tralau T, Heidler J, et al. Allergic contact dermatitis: epidemiology, molecular mechanisms, in vitro methods and regulatory aspects. Cellular and Molecular Life Sciences. 2012;69(5):763-81
  2. DeKoven JG, Warshaw EM, Zug KA, et al. North American Contact Dermatitis Group patch test results: 2015–2016. Dermatitis. 2018;29(6):297-309
  3. Krasteva M, Kehren J, Ducluzeau MT, et al. Contact dermatitis II. Clinical aspects and diagnosis. European Journal of Dermatology. 1999;9(2):144-60.
  4. Frings VG, Böer-Auer A, Breuer K. Histomorphology and immunophenotype of eczematous skin lesions revisited—skin biopsies are not reliable in differentiating allergic contact dermatitis, irritant contact dermatitis, and atopic dermatitis. The American Journal of Dermatopathology. 2018;40(1):7-16.
  5. American Contact Dermatitis Society. Contact Allergen Management Program. 2019. Available at: https://www.contactderm.org. Accessed August 25, 2019.
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