There are two types of contact dermatitis – irritant and allergic.
Irritant contact dermatitis is caused by direct contact with a substance which irritates the skin. It most commonly affects the hands. A patch of skin may become sore after being in contact with an irritating substance which causes some skin damage. Once the initial damage has occurred, the skin is more easily affected by other irritants. This leads to further inflammation, even in small amounts.
Some of the most common irritants are:
- Water - hands being exposed to water for long periods of time. It is most common when the water is hard, chalky, or contains a lot of chlorine.
- Detergents - such as soaps and bleach. People who do a lot of cleaning are prone to irritant contact dermatitis.
- Solvents - like chemicals used in various places of work such as petrol and oils.
- Acids - such as alkalis and cement.
- Powders - including dust and soil.
- Plants - like ranunculus, anemone, clematis, hellebore, and mustards.
Allergic contact dermatits
occurs when your immune system reacts against a specific allergen. Only a small amount of allergen coming in contact with your skin can cause a rash.
These are not allergies you are born with. You must have previously come into contact with the allergen which has sensitized your immune system. Once sensitized, your skin reacts and becomes inflamed when it comes into further contact with the allergen. This is why you can suddenly develop a skin allergy to something you have come into contact with many times before. It is not clear why some people become allergic to some substances and others do not.
Some of the most common allergens are:
- Nickel – the most common cause. It occurs in many types of metals found in jewelry, studs in jeans, and on other clothes like bra straps. It is common to develop itchy red patches on the skin next to these things.
- Cobalt – traces can be found in some jewelry.
- Chromate – a metal found in cement.
- Cosmetics – particularly perfumes, hair dyes, preservatives, and nail varnish resins.
- Additives – to shoes and close made of leather and rubber.
- Preservatives - added in creams and ointments.
- Plants – the most common culprits being chrysanthemums, sunflowers, daffodils, tulips and primula.