Contact dermatitis occurs when your skin reacts to a particular substance.
This can be either:
an irritant – a substance that directly damages the outer layer of skin
an allergen – a substance that causes your immune system to respond in a way that affects the skin
Irritant contact dermatitis
Irritant contact dermatitis may be caused by frequent exposure to a weak irritant, such as soap or detergent. It may also develop if you've been in contact with a stronger irritant for a short while.
You're at an increased risk of irritant contact dermatitis if you also have atopic eczema, which is the most common form of eczema.
Common irritants include:
soaps and detergents
antiseptics and antibacterials
perfumes and preservatives in toiletries or cosmetics
oils used in machines
acids and alkalis
powders, dust and soil
water – especially hard, chalky water or heavily chlorinated water
many plants – such as Ranunculus, spurge, Boraginaceae and mustards
If you already have irritant contact dermatitis symptoms, they can be made worse by heat, cold, friction (rubbing against the irritant) and low humidity (dry air).
Exposure at work
You may be more at risk of irritant contact dermatitis if you work with irritants as part of your job, or if your job involves a lot of wet work.
If you develop the condition because of a substance you work with, it may be referred to as occupational irritant dermatitis.
This type of dermatitis is more common in certain occupations, including:
beauticians and hairdressers
cooks and caterers
metal and electronics workers
health and social care workers
mechanics and vehicle assemblers
Allergic contact dermatitis
The first time you come into contact with an allergen, your body becomes sensitised to it, but does not react to it. It's only when you're exposed to the substance again that your immune system reacts and causes the skin to become red and itchy.
Allergens that commonly cause allergic contact dermatitis include:
cosmetic ingredients – such as preservatives, fragrances, hair dye and nail varnish hardeners