Inflammation of the affected tissue is present in the epidermis (the outermost layer of skin) and the outer dermis (the layer beneath the epidermis).Contact dermatitis results in large, burning, and itchy rashes. These can take anywhere from several days to weeks to heal. This differentiates it from contact urticaria (hives), in which a rash appears within minutes of exposure and then fades away within minutes to hours. Even after days, contact dermatitis fades only if the skin no longer comes in contact with the allergen or irritant. Chronic contact dermatitis can develop when the removal of the offending agent no longer provides expected relief. Irritant dermatitis is usually confined to the area where the trigger actually touched the skin, whereas allergic dermatitis may be more widespread on the skin. Irritant dermatitis usually found on hands whereas exposed areas of skin. Symptoms of both forms include the following:

Red rash. This is the usual reaction. The rash appears immediately in irritant contact dermatitis; in allergic contact dermatitis, the rash sometimes does not appear until 24–72 hours after exposure to the allergen. Blisters or wheals. Blisters, wheals (welts), and urticaria (hives) often form in a pattern where skin was directly exposed to the allergen or irritant. Itchy, burning skin. Irritant contact dermatitis tends to be more painful than itchy, while allergic contact dermatitis often itches. The surface appearance of skin is dry and fissured in the irritant contact dermatitis whereas vesicles and bullae are seen in allergic contact dermatitis.
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.