The direct contact of an irritant substance with the skin can produce contact dermatitis. In most cases this sensitivity to a substance is peculiar to the individual and therefore has an allergic basis. Some examples of irritants are soaps, hair dyes, and nickel (as in buckles and necklaces). When contact with the irritant substance is primarily at the place of employment the condition is described as industrial or occupational dermatitis.
A careful examination of the history of a patient is necessary to discover the most likely cause of the dermatitis. The cause may be confirmed by patch testing, which involves exposing an area of the skin to the suspected substance in order to determine the reaction. The most important part of the treatment is to avoid the irritant. Also various creams or lotions can be applied directly to the affected area, usually resulting in rapid recovery.
Napkin dermatitis
Also known as ammoniacal dermatitis, napkin dermatitis is caused by direct chemical irritation to the skin by urine-soaked nappies. The inflammation is mainly restricted to the groin and buttock area. The irritant chemical is ammonia, normally not present in the urine but produced from the breakdown of urea by bacteria. The skin within the creases of the groin and buttock are normally not involved (these areas are spared from direct contact with the urine), which distinguishes this condition (commonly called ‘nappy rash’) from others such as seborrhoeic dermatitis and atopic dermatitis.
The treatment is to rinse the nappies without using soaps or detergents, but with a mild antiseptic (for example, boracic acid) that will control the growth of bacteria. A protective cream such as lanoline or zinc oxide also helps to prevent the condition.
Scaling of the scalp is the typical condition of seborrhoeic dermatitis. The scaling also frequently occurs on the chest and armpits. This form of dermatitis is caused when sebaceous gland activity increases during and shortly after puberty. This build up of sebum increases the likelihood of greasy skin, scaling (dandruff is a form of seborrhoeic dermatitis), and secondary bacterial infection of blocked skin pores which produces acne vulgaris. For those with an inherited tendency to persistent sebaceous gland overactivity, these conditions may be present throughout life.
The most common feature is patchy areas of dermatitis that appear and disappear over long periods of time. These areas are muck more prone to infection by invading bacteria. Psychological factor such as mental stress may also produce ‘flare-ups’ of the condition.
To control the problem various anti-inflammatory lotions and creams are used. Also certain creams that prevent the build-up of sebum are often used in between the major attacks.
Atopic dermatitis
Also called atopic eczema and infantile eczema, atopic dermatitis is a fairly common condition. People who are atopic have an inherited predisposition to allergies such as asthma and hay fever, and often have two or more allergies.
Atopic dermatitis usually first develops relatively early in life. Most cases develop by the end of the first year of life and then persist in varying degrees throughout childhood, often disappearing before adolescence. However the tendency to ‘atopy’ will persist and the dermatitis will occur occasionally throughout adult life, or re-develop unexpectedly. Viral infections (especially Herpes simplex and those which follow vaccination against smallpox) commonly trigger off atopic dermatitis.
One of the common features is ‘cradle cap’, a localized scaling round the head and neck. The condition may be confirmed if there is a history of atopic dermatitis or other allergy-based conditions in other members of the family.
The areas most frequently affected are the head and cheeks, then the backs of the knees, the elbow region, and the neck. A raised scaly area develops first, followed by the appearance of small red lumps. These lumps usually break open and weep. The area becomes extremely itchy and scratching often increases the inflammation.
Treatment is mainly of the symptoms and usually involves the use of various anti-inflammatory and anti-itch creams and lotions.
Neurodermatitis
The condition which begins as a minor skin reaction with scratching and eventually becomes an unconscious habit is described as neurodermatitis. Persistent scratching produces a reddened area that becomes thick and scarred (lichenified).
As the habit of scratching is often difficult to break, treatment includes specific anti-itch tablets and creams, sometimes sedative drugs, and occlusive dressings. Supportive psychotherapy may also be needed.
