The recognition of skin disorders is essentially a visual art. It requires experience to distinguish what is dermatitis or eczema from what is not; disorders that might be confused with dermatitis or eczema include such conditions as diffuse skin malignancies, known as reticuloses, or infections either fungal or parasitic.

Dermatitis which develops in response to contact with a foreign, but not necessarily a newly-contacted, substance is called Contact Dermatitis. There are two broad types: the irritant, and the allergic.

Clothing Apart from rubber there are a variety of other potential sensitizers in clothes. The pattern of eczema follows the area covered by the offending garment, with accentuation Of the eruption in moist zones and those at which the garment makes closest contact with the skin. The responsible chemicals include dyes (which may cross-react with PPD), formaldehyde and other garment finishes. Shoe dermatitis may be caused by these chemicals, also by those in leather and glues.

Cosmetic dermatitis is probably more common than dermatologists suppose, since most women who find that one cosmetic causes them trouble will simply change to another without seeking medical advice. The principal trouble-makers are perfumes, which contain an array of plant extracts, animal oils and synthetic chemicals.

Nail varnish causes contact dermatitis, not on the fingers but where the nails touch the skin, mainly around the eyes and neck. Lipstick sometimes causes contact dermatitis due to eosin or other dyes. Hair dyes which contain PPD or related compounds may cause dermatitis, which is chiefly seen round the hair line. Finally lanolin and some preservatives in creams and ointments may also cause contact dermatitis reactions.

Plants A few plants are powerful sensitizers and well known for causing contact dermatitis. Poison ivy is the most famous in the United States, as is the primula in the United Kingdom. Chrysanthemum and tulip bulbs may sensitize a few people. In Australia the Rhus tree, a close relative of poison ivy, has leaves which provoke a very severe dermatitis in many people. The resulting rash —which may occur where the skin has touched the plant, or on a face which has been touched by contaminated hands—has a streaked appearance.

Medicaments Contact dermatitis as a reaction to a medicament is confusing, since presumably the skin was abnormal before it was applied. The principal causes of such reactions are antibiotics, anti-histammes, local anaesthetics, ointment bases (such as lanolin), ointment preservatives (such as para bens), and stabilizers (such as ethylene diamine).

The number of other possible skin sensitizers is enormous. Other important ones include epoxy-resin, plastic hardeners, formaldehyde resins, pesticides and fungicides.

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