Contact dermatitis

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Contact dermatitis

Inflammatory response of skin to contact with an external antigen or irritant.

Two mechanisms/types:
1) Irritant contact dermatitis (ICD) – 80% of cases
2) Immunologic allergic contact dermatitis (ACD) – 20% of cases

Irritant contact dermatitis:
Any substance has the potential to be an irritant under the right circumstances.
Irritants produce direct toxic injury to the skin (response is not immune mediated)

Acute eruption – single exposure from strong toxic chemical (eg acid)  erythema, vesicles, bullae, skin sloughing – sharp well defined borders; occur from a few minutes to hours after exposure.

Chronic cumulative insult reaction – more common; due to multiple exposures to low level irritants (eg soaps); takes from weeks to years to develop; characterised by erythema, scaling, pruritis, fissuring, lichenification – poorly defined borders

Immunologic allergic contact dermatitis (ACD):
Type IV delayed, cell mediated, hypersensitivity reaction. Initial exposure sensitises patients and then 48-72 hours after re-exposure to antigen  inflammatory reaction

Acute ACD – erythema, vesicles, pruritis; usually spreads beyond the area of contact (eg poison ivy dermatitis)

Chronic ACD – (appear similar to chronic ICD) – pruritis, erythema, lichenification and excoriated

Foot contact dermatitis:
Can take any form of ACD (rare) or ICD
In foot interdigital spaces not affected (will be affected if tinea)
Plantar surface can be affected, but is not as sensitive as other areas

Shoe dermatitis:
• tends to be patchy, so not necessarily bilateral
• secondary infection can occur
• most commonly due to rubber accelerators, adhesives and dichromates in leather.

Patch testing:
Can confirm diagnosis

Two commonly used methods:
1) Finn chamber
A small amount of allergen in a medium (usually petroleum jelly) is placed into small individual pots affixed to a piece of paper baking and adhered to skin.

2) True test system
The allergens are already impregnated in commercially available tape (limited number of allergens available)

The strips from both methods are applied to the forearm skin and checked after 48 hours – may need to monitor for longer for allergic reaction

Management:
Identify and remove cause so contact is avoided
Wet dressings for vesicles
Astringent soaks (eg Burows solution)
Topical corticosteroids for pruritis
increased aeration (cotton or wool socks; avoid shoes with plastic uppers)
May need antibiotics for secondary bacterial infection
May need emollients for help with any lichenification and/or fissuring

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