Dermatitis means an inflammation of the skin. Contact dermatitis is a term used when this inflammation is caused by contact with something in the environment. The changes of dermatitis seen in the skin take the form of eczema; hence it may sometimes be referred to as contact eczema but may have nothing to do with atopic tendencies and atopic eczema.
Two main groups of things in the environment cause contact dermatitis, irritants and allergens.
Irritants are substances like detergents and solvents that strip the skin of its natural oils, and cause dermatitis to develop if contacted frequently and without skin protection. When this happens, the skin changes are known as an irritant contact dermatitis. The most important factor in causing this type of contact dermatitis is the amount of irritants to which you are exposed. It is particularly common in people who do a lot of wet work (especially in hand dermatitis), e.g. nurses, hairdressers, those who work in bars, and those in the catering trade.
Allergens are things to which your immune system can develop a specific reaction after you have come into contact with them. Examples include substances such as nickel, rubber, and perfumes or preservatives used in some creams and cosmetics. This type of dermatitis is called an allergic contact dermatitis. It is not known why some people who are exposed to these allergens develop it while others do not.
Sometimes substances such as proteins in fruit and vegetables, when touched, can cause an immediate allergic reaction leading to itchy skin swellings known as contact urticaria (hives), which in turn can aggravate your dermatitis.