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Phototherapy is typically performed by a dermatologist. Depending on the type of phototherapy used and how extensive it will be, it may be performed in the dermatologist’s office or in a medical center. It is generally recommended that patients avoid sunbathing before and during phototherapy, and certain medications that affect light sensitivity (e.g., retinoids) may or may not need to be altered. Patients may also be advised to limit alcohol consumption. It is important to follow a physician’s orders.

The doses of ultraviolet radiation used in phototherapy may be determined by the patient’s skin type, but skin type alone does not always reflect the actual sensitivity of a person. Because of this, phototesting may be performed at either a dermatologist’s office or a medical center before phototherapy is recommended. This is done by exposing six small areas of skin that are not usually exposed to the sun (e.g., lower back, buttocks) to a gradually increasing series of light exposure. The doses of light used and the increments between them depend upon the patient’s skin type and the method of phototherapy. Phototesting may take several days. Sunbathing or exposure to sunlamps must be avoided before and during phototesting.

When topical agents are used in combination with ultraviolet B light, they are generally applied for a period of time that varies depending on the agent used. For example, a coal tar preparation is generally left on the skin for about an hour. The agents are typically wiped off of the skin before ultraviolet exposure.

When psoralens plus ultraviolet A light (PUVA) is used, the drugs are administered before light exposure. The delay between the time that the psoralens are administered and the exposure to light depends on the form of application. Oral psoralens are usually taken about 90 minutes before ultraviolet exposure. In bath PUVA, the patient soaks in psoralen-solution bath water for 15 to 20 minutes immediately before exposure.

Depending on the condition treated, the patient may be exposed to light over the entire body surface, only select areas of the body may be exposed, or the patient’s extremities (e.g., arms, legs) may be exposed to higher doses than the trunk.

Ultraviolet light may be administered through a booth, bed (similar to a tanning bed) or handheld device operated by a dermatologist. The genitals are protected, especially in men. Uninvolved skin should also be protected with sunscreen or covered with cloth. The session may take from about 30 minutes to a couple of hours, depending on the type of phototherapy being used and the condition being treated.

Ultraviolet light is generally given in doses that produce slight erythema (redness). With repeated exposures, a gradual increase of the dose is required to maintain this reaction. Protective eyewear is required if psoralens are used. This eyewear must block 100 percent of ultraviolet light and must be worn for 24 hours after the medication has been taken when outdoors, near bright windows or under fluorescent lighting.

Doses may be increased with each successive treatment and the rate of increase depends on treatment frequency and the outcome of the previous treatment. In treatment without psoralens, doses may be increased with every other treatment. In treatment with psoralens, doses are increased no more often than twice a week, at least 72 hours apart, and never in the first week of treatment. If performed properly and in adequate doses, side effects are generally mild. The dermatologist performing the phototherapy will check for these. If intense or painful erythema develops, exposures are stopped until these symptoms disappear.

Usually, phototherapy treatment is continued until complete remission is achieved or no further improvements can be obtained.

Maintenance treatments may lead to longer remission times and are used in the treatment of many conditions, including psoriasis. These may last a few months to a year. The last effective dose is typically given throughout maintenance and, if a relapse occurs during this time, doses are increased again until the condition clears.

To be effective, phototherapy must be given consistently over scheduled periods of time. As a result, it is essential for patients to keep all of their scheduled maintenance appointments. Ideally, treatments should be scheduled for the same time of day.

Repeated skin examinations are very important after phototherapy. These check for any adverse conditions that may develop, such as carcinoma. Such conditions may occur many years after treatment ends.

Although phototherapy sessions usually begin at a medical facility, some patients may be able to continue the treatments at home. Home phototherapy with a prescription light box provides a convenient alternative for patients. However, patients must closely follow their physician’s instructions for use. Failing to adhere to the physician’s schedule can reduce the effectiveness of the treatment. Patients must also be sure to take all of the usual precautions, such as protecting the eyes and genitals. Patients undergoing home phototherapy will also have to visit their physician for regular examinations.