Allergic Contact Dermatitis

Essentials

• It is often not possible to differentiate allergic contact dermatitis from other types of dermatitis on the basis of clinical presentation alone.
• The diagnostic cornerstones are clinically established eczema, contact allergy and temporally-related exposure to the allergen in question.
• The possibility of allergic contact dermatitis should be borne in mind where dermatitis is not resolving despite appropriate treatment.

Aetiology

• Delayed cell-mediated allergy (skin contact allergy)
• Usually results from a long-standing exposure.
• The most common causative agents http://www.dynamed.com/condition/contact-dermatitis#CAUSES_OF_ALLERGIC_CONTACT_DERMATITIS are nickel (picture ) as well as perfumes and preservatives used in cosmetics and hygiene products.
• Other causative agents include chemicals found in rubber, ingredients of plastics and glues (picture ), chromium and cobalt compounds as well as ingredients used in skin care products.
• Plants may, also, cause allergic contact dermatitis (e.g. Primula obconica) (picture ) or photodermatitis Photodermatitis (picture ).

Symptoms

• Usually first appear at the site of exposure but may become more widespread (pictures ) http://www.dynamed.com/condition/contact-dermatitis#TOPIC_LX3_NQS_MMB, unlike irritant contact dermatitis that appears only in the areas of skin where irritation has occurred.
• After subsequent exposure, the symptoms will redevelop within 1-2 days and will gradually resolve as the exposure ceases.

Diagnosis

• The site of the rash should prompt a suspicion of allergic contact dermatitis, particularly when located at the following sites:
  • hands and wrists (metal, leather, working tools, chemicals; picture ).
  • armpits (deodorants)
• Allergic dermatitis may, however, occur anywhere on the body. Typical sites include:
  • face (pictures ) and neck (picture ; skin care products, cosmetics)
  • waist (leather, metal; pictures )
  • gluteal cleft (haemorrhoid creams and suppositories)
  • thighs and legs (socks, rubber boots, topical treatments for leg ulcers)
  • feet (metals, rubber, leather, dyes, contact glue, chromium, antimycotics).

Investigations

• Patch testing is usually not indicated if the history clearly identifies the causative allergen, for example nickel.
• The diagnostics of skin contact allergy and allergic dermatitis use epicutaneous tests (patch testing Diagnostic Tests in Dermatology) http://www.dynamed.com/condition/contact-dermatitis#EPICUTANEOUS_PATCH_TESTING, which demonstrate possible sensitisation to allergens.
• However, a positive test result does not always prove the causal relationship with the patient's dermatitis.
• Testing is carried out and interpreted by a dermatologist.

TreatmentEmollients and Moisturisers for Eczema, Topical Pimecrolimus for Eczema

• The definitive treatment of allergic contact dermatitis is the avoidance or removal of the allergen (personal protective equipment, changing substances or methods used at the workplace, change of employment).
• Topical glucocorticoid creams
• Systemic treatments for eczematous conditions are used in chronic and difficult cases at the discretion of a dermatologist.

Immediate contact dermatitis

• Unlike allergic dermatitis (delayed allergy), this is based on an immediate, IgE-mediated allergy
• Contact urticaria and protein contact dermatitis
• Redness, pruritus and/or urticaria develop immediately (less than 30 minutes) at the site of the allergen contact. Allergens include natural rubber (latex), cat or dog (dander or hair), root and other vegetables.
• Clearly more rare than allergic contact dermatitis, but in its chronic state its appearance may resemble that of allergic dermatitis.

Specialist consultation

• Consult a dermatologist in particularly severe and extensive cases as well as chronic forms of the conditions
• Patch testing and the verification of diagnosis
• A suspicion of occupational allergic contact dermatitis or hand dermatitis

Pictures