Contact Dermatitis - Eczema

Contact Dermatitis

·        May be irritant or allergic or both.  May co-exist with endogenous forms (eg atopic) 

·        Differentiate from endogenous on the basis of history, distribution and maybe allergy testing, not morphology

Contact Irritant Dermatitis

·        Irritant: a substance which induces dermatitis in anyone if applied in sufficient concentration for long enough ® penetrates skin and produces cellular damage

·        Individuals vary in their threshold 

·        Heat and ­ or ¯ hydration impair barrier function ® more susceptible

·        Cumulative effect of different irritants

·        Irritants include: acids, alkalis, solvents, soaps, detergents, enzymes, abrasives

·        Diagnosis:

o  Exposure to irritants for what length of time and frequency

o  Are sites consistent with exposure

o  Does it improve after exposure stops 

o  Can contact allergy be excluded (eg have they had it since childhood Þ more likely to be allergy)

·        Management:

o  Steroid creams, emollients 

o  Reduce exposure, remove occlusion (ie sweat inside gloves ® over hydration), other work

Contact Allergic Dermatitis

·        Type 4 cell mediated immune reaction (see Allergy and Hypersensitivity Disorders) 

·        Often takes repeated exposure, so no previous symptoms may not be significant (same for type 1 reactions). Eg may have worn rubber gloves for years 

·        Once sensitised, further exposure to even minuscule amounts ® reaction after a day or two. Takes 24 –       72 hours, compared to type 1 which takes 15 – 20 minutes

·        Will involve primary sites, and maybe distant sites (eg eyes, genitals)

·        Photoallergy = need exposure to allergen + UV light to cause rash.  Eg sunscreens 

·        Common allergens: nickel (eg pierced ears), rubber additives, plants, chromate in cement, hairdressing chemicals, perfumes, …

·        Rubber glove allergy can be:

o  Type 1 due to rubber

o  Type 4 due to rubber additives 

o  Contact dermatitis due to sweaty hands - ­ risk of type 1 or 4 reaction (mediated by Langerhans cells) due to ¯ barrier function

·        Diagnosis:

o   Exposure to possible allergens 

o   Sites consistent with exposure, goes away when exposure stops. NB some sites resistant (scalp, soles)

o   Patch testing

·        Management:

o   Steroids, emollients, etc

o   Avoid exposure