Sometimes people develop a rash because of something which has come into contact with their skin and this is known as contact dermatitis or contact eczema. Most of the time the rash occurs because the skin has come into contact with an irritant (for example overuse of soaps or alcohol gels) but sometimes the rash develops due to an allergy, when it is known as a contact allergic dermatitis. Irritant reactions tend to appear almost immediately while allergic reactions tend to appear a bit later - for example, a few days after using a new moisturiser. If the skin has been in contact with the allergen before, the reaction may be faster.
Many contact allergens are found in everyday life and include:
Nickel, one of the most common contact allergens. It is a is metal which is often found in costume jewellery, belt buckles and cheap silver
Fragrance ingredients. These are found in numerous products which you may be exposed to day to day including perfumes, shampoos and cleaning products.
Paraphenylene diamine, also known as PPD is found in hair dyes and can cause problems even if you have coloured your hair for many years.
It is also the cause of allergic reactions to black henna used in some temporary tattoos
Sometimes it is difficult to know exactly what has caused a skin reaction but if a contact allergic dermatitis is suspected, you may be referred for patch testing to help identify a potential trigger.
The mainstay of treatment is to avoid contact with the substance causing the eczema. Acute episodes may require treatment with steroid creams or in severe cases you may be prescribed steroid tablets.