It is important to also note that chemicals sometimes have several different names, and do not always appear on labels.The distinction between the various types of contact dermatitis is based on a number of factors. The morphology of the tissues, the histology, and immunologic findings are all used in diagnosis of the form of the condition. However, as suggested previously, there is some confusion in the distinction of the different forms of contact dermatitis. Using histology on its own is insufficient, as these findings have been acknowledged not to distinguish, and even positive patch testing does not rule out the existence of an irritant form of dermatitis as well as an immunological one. Prevention
In an industrial setting the employer has a duty of care to its worker to provide the correct level of safety equipment to mitigate exposure to harmful irritants. This can take the form of protective clothing, gloves, or barrier cream, depending on the working environment. It is impossible to eliminate the complete exposure to harmful irritants but can be avoided using the multidimensional approach. The multidimensional approach includes eight basic elements to follow. They are:

Identification of possible cutaneous irritants and allergens
To avoid skin exposure, use appropriate control measures or chemical substitutes. Personal protection can be achieved by the use of protective clothes or barrier creams.
The mechanism of action varies from toxin to toxin, but is usually due to the production of a photoproduct. Toxins which are associated with PCD include the psoralens. Psoralens are in fact used therapeutically for the treatment of psoriasis, eczema, and vitiligo. Photocontact dermatitis is another condition in which the distinction between forms of contact dermatitis is not clear-cut. Immunological mechanisms can also play a part, causing a response similar to ACD. Diagnosis
Since contact dermatitis relies on an irritant or an allergen to initiate the reaction, it is important for the patient to identify the responsible agent and avoid it. This can be accomplished by having patch tests, one of various methods commonly known as allergy testing. The patch tests were based on the concept of a type IV hypersensitivity reaction where there is exposure of allergens to skin and checking for the development of contact dermatitis in that area. This test involves the application of suspected irritant to a part of the skin and cover it with impermeable material and attached to the skin with the help of adhesive plaster. The top three allergens found in patch tests from 2005 to 2006 were:  nickel sulfate (19.0%), Myroxylon pereirae (Balsam of Peru, 11.9%), and fragrance mix I (11.5%).The patient must know where the irritant or allergen is found to be able to avoid it.