Contact Dermatitis Health Article

Photo contact dermatitis

In photo contact dermatitis, certain substances undergo chemical changes as a result of exposure to light that transform them into either irritants or allergens. Aftershave lotions, sunscreens, and certain topical sulfa drugs may be changed into allergens, while coal tar and certain oils used in manufacturing may become irritants after light exposure.

When to call the doctor

Contact dermatitis is not a medical emergency. It can often be treated at home once the irritant or allergen has been identified. A visit to the doctor may be necessary, however, in order to identify the cause(s) as well as obtain specific recommendations for treatment.

Diagnosis

Diagnosis of contact dermatitis begins with a physical examination and asking the patient questions about his or her health and daily activities. When contact dermatitis is suspected, the doctor attempts to learn as much as possible about the child or adolescent's school, sports participation, hobbies, favorite jewelry, use of medications and cosmetics—anything that might shed light on the source of the problem. The doctor will ask when the symptoms started, whether this is the first time they occurred, whether the rash is spreading, whether the primary sensation is itching or burning, and how severe the itching or burning feels.

In some cases, an examination of the home or school may be undertaken; in one interesting case, the doctors discovered that a rash on the back of the child's thighs was an allergic reaction to nickel in the metal parts of the chairs in the child's school. If the dermatitis is mild, responds well to treatment, and does not recur, ordinarily the investigation is at an end. More difficult cases require patch testing to identify the specific allergen.

Two methods of patch testing are used in the early 2000s. The most widely used method, the Finn chamber method, employs a multiwell aluminum patch. Each well is filled with a small amount of the allergen being tested and the patch is taped to normal skin on the patient's upper back. After 48 hours, the patch is removed and an initial reading is taken. A second reading is made a few days later.

The second method of patch testing involves applying a small amount of the test substance to directly to normal skin and covering it with a dressing that keeps air out and keeps the test substance in (occlusive dressing). After 48 hours, the dressing is taken off to see if a reaction has occurred. Identifying the allergen may require repeated testing, can take weeks or months, and is not always successful. Moreover, patch testing works only with ACD, though it is considered an essential step in ruling out ICD.

In a few cases, the doctor may take a skin biopsy in order to rule out certain infectious skin diseases.