What is allergic contact eczema?

Allergic contact eczema is a form of Type IV hypersensitivity reaction. Hypersensitivity means that the immune system is stimulated a lot by only minor triggers or triggers that shouldn't elicit an immune response (true allergy is a Type I hypersensitivity reaction). In contrast to atopic eczema, which is due to histamine being released by mast cells triggered by IgE, a Type IV hypersensitivity reaction occurs because other types of white blood cell are involved. The reaction requires you to have been sensitised to the allergen before – meaning that you have to have been exposed to it for a first time, which did not cause any symptoms. The reaction is very specific to a particular allergen, and will not develop if you touch other allergens.

Common allergens include the following chemicals:

  • Nickel, which is found in jewellery, bra clips, and studs in jeans.
  • Dichromate, which is found in chrome-tanned leather, cement, and matches.
  • Rubber chemicals, which can be found in many items, such as shoes and tyres.
  • Rosin, which is a type of solid resin from pines and conifer trees. This can be found in plasters. Epoxy resin can also be a common allergen.
  • Paraphenylenediamine, which is found in hair dyes.
  • Urushiol, which is found on poison ivy, poison oak, poison sumac, and Japanese lacquer trees.
  • Balsam or Peru, which is found in perfumes and also in some citrus fruits.
  • Neomycin and benzocaine, which might be in certain creams. Parabens are chemicals used as preservatives in creams and cosmetics.

It is important to keep track of where the original rash was before it spreads to other parts of the body, as this can provide a good idea regarding what you touched. It can develop several hours after you have touched your allergen.

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