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AlexanderSalava

Allergic Contact Dermatitis

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.

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 1) 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 2), 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 10) or photodermatitis Photodermatitis (picture 11).

Usually first appear at the site of exposure but may become more widespread (pictures 3 4) 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.

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 2).
- armpits (deodorants)
Allergic dermatitis may, however, occur anywhere on the body. Typical sites include:
- face (pictures 5 6) and neck (picture 7; skin care products, cosmetics)
- waist (leather, metal; pictures 1 8)
- 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).

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.

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.

Treatment of allergic contact dermatitis in hands: see Hand Dermatitis.
Moderately potent to potent glucocorticoid creams http://www.dynamed.com/condition/contact-dermatitis#TOPIC_HTV_F2R_XLB once or twice daily until the skin has healed, for 2-6 weeks as appropriate to the severity of dermatitis. A follow-up appointment is indicated if the condition has not resolved.
In acute vesicular dermatitis relief can often be obtained with moist compresses (10-20 minutes twice or thrice daily).

In cases of severe and spreading allergic contact dermatitis a short course of systemic glucocorticoids http://www.dynamed.com/condition/contact-dermatitis#TOPIC_TXF_D2R_XLB may be indicated, e.g. prednisolone 20-40 mg once daily for 1-2 weeks.
Antimicrobials are very rarely needed in allergic dermatitis, and they do not replace topical treatment. If the rash is clearly infected (picture 9), an antimicrobial may be indicated (cephalexin 500 mg three times daily for 7-10 days).

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.

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

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