Inflammatory skin reaction (dermatitis) to an external agent. This can either be an irritant or an allergen.
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Allergic contact dermatitis is a type IV (delayed) hypersensitivity reaction that occurs after sensitization and subsequent re-exposure
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Irritant contact dermatitis occurs after damage to the skin, usually by chemical irritation.
Epidemiology
- Accounts for around 6% of all dermatology consultations. Many are referrals from occupational health. Around 80% are irritant dermatitis.
Aetiology
Mechanism of type IV allergic reaction
This animation from America, is better than I can explain it.
Presentation/Assessment
- There may be a few differences between allergic and irritant dermatitis (in reality, this can be more difficult to distinguish and both can present in the same way)
- Irritant contact dermatitis can be burning, stinging, sore; whereas allergic dermatitis mainly present with redness and itching (and scaling).
- Irritant dermatitis is usually well demarcated in the acute phase (less so with allergic forms)
- Depending on the suspected cause, the pattern of distribution of the dermatitis may tend towards a diagnosis of either irritant or allergic pathology
- e.g. the neck/face are commonly affected in cosmetic allergies, whereas the hands are often exposed more to irritants
- Irritant contact dermatitis can also be associated with atopic eczema (unlike allergic)
- In general, both can present with
- red skin; a vesicular/papular rash; crusting/scaling; itch, pain or burning
- if exposure and the reaction is chronic, then fissures, lichenification and hyperpigmentation may also be present
- The patient history is very important
- Any triggers/exacerbating/alleviating factors? Are there times when the symptoms are worse/better? Describe the onset, progression etc?
- Occupation/hobbies?
- Any young children?
- Any changes in perfume/washing detergent etc?
- Any pre-existing skin disease?
- Any other medical conditions/drugs/allergies?
- Any family hx of skin disease/allergy?
- NB If anything does stand out in the history, always ask more about this.
Investigations
- Patch-testing is the gold standard and should be done in cases with
- chronic, recurring, or unrelenting eczematous or lichenified dermatitis (occupational or otherwise) despite appropriate avoidance measures and corticosteroid treatment
- features suspicious of contact dermatitis but no clear history of relevant exposure
Management
- Avoidance of the the trigger stimulus should be advised
- Sometimes it is not possible to completely remove the stimulus
- Advise the frequent use of emolients to maintain skin hydration, and try to avoid soap by substituting with aqueous cream
- Topical steroid may be used to reduce symptoms (strength should be appropriate to the severity/duration/location of the symptoms)
- Whilst antihistamines aren’t recommended by NICE, they may help some patients with severe itch.
- Light therapy (PUVA) and non-steroid immunomodulation is rarely required and should only be considered by a specialist after conventional measures have failed.