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
·
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
· 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
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