Contact Dermatitis

Inflammatory skin reaction (dermatitis) to an external agent.  This can either be an irritant or an allergen.

  • Allergic contact dermatitis is a type IV (delayed) hypersensitivity reaction that occurs after sensitization and subsequent re-exposure

  • Irritant contact dermatitis occurs after damage to the skin, usually by chemical irritation.



  • Accounts for around 6% of all dermatology consultations.  Many are referrals from occupational health.  Around 80% are irritant dermatitis.



Mechanism of type IV allergic reaction

This animation from America, is better than I can explain it.


  • 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)Pioneer11-male
  • 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.


  • 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


  • 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.

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