Photodynamic therapy

Photodynamic therapy (PDT) is a treatment for pre-cancerous, sun damaged skin (which may one day turn into a skin cancer) and some types of skin cancers.

There are two methods used for PDT. One uses a special red light lamp (conventional lamp PDT) and the other method uses natural sunlight (daylight PDT). In both cases a photosensitising cream is applied to the affected area of skin. This is absorbed by abnormal cells, leaving healthy skin unaffected. The red light or natural sunlight is then used to activate the cream and kill the abnormal cells in the skin.

What does conventional lamp PDT involve?

Conventional lamp PDT is an outpatient procedure completed by your consultant and our dermatology nurse and used to treat small, specific areas or lesions on the skin.

24 hours before you come for your treatment, please do not apply any sunscreen, moisturiser or other skin products, including vaseline and make-up, to the area due to be treated as these may affect the PDT treatment

The first step is to prepare the skin for treatment. This will involve cleansing of the skin and, if necessary, removal of any scale or crusts on the area.

The photosensitising cream is then applied to the area and covered with an occlusive dressing. This needs to remain in place for 3 hours. You are free to leave the clinic and return or relax in our waiting room during this time. This wait is to allow the photosensitiser to be absorbed and to convert into the active chemical within the skin.

After 3 hours the cream is then wiped off and the area cleaned. A bright red light is shone onto the treatment area for a minimum of 10 minutes (the time may increase if we need to reduce the intensity of the light due to patient comfort). After the treatment has been completed, a dressing will be applied for a minimum of 2 days to prevent further exposure to light.

After treatment, your nurse will give you instructions on what to expect and how to care for your skin. After a few days the area may weep a little and crust. This is normal so do not be alarmed. A dressing can be left on for longer if it is required. Healing takes place under the crust so do not disturb it. The crust will eventually fall off naturally once the area underneath has healed. This can take as long as 7-10 days.

What does daylight PDT involve?

Daylight PDT is an outpatient procedure which is used to treat pre-cancerous skin lesions. The principle is the same as conventional lamp PDT but the method is slightly different. Daylight PDT is best for large areas of sun damaged skin, or pre cancerous skin lesions such as actinic keratosis.

Before you come for your treatment, please do not apply any sunscreen, moisturiser or other skin products, including vaseline or make-up, to the area due to be treated as these may affect the PDT treatment

The first step is the nurse will apply a chemical sunscreen to the area to be treated and any other areas which will be exposed to sunlight during the treatment. This will protect your skin from UV light but not the wavelength required for the treatment (daylight). This will be left for 15 - 20 minutes to soak into the skin.

Next your consultant and nurse will prepare the skin by degreasing and removing any overlying crusty skin. The photosensitising cream will be applied to the area of treatment and left uncovered.

You will then be asked to sit outside in the natural sunlight for 2 hours. This activates the cream which begins to destroy the damaged cells. Even on an overcast day there is enough daylight for the treatment to work.

After 2 hours the nurse will remove any remaining gel and apply a sunscreen to the affected area. Sun exposure should be avoided for the next 2 days so we advise regular application of sunscreen and physical cover up with clothing or a hat.

Your nurse will give you instructions on how to care for your skin afterwards. You may shower and bathe as normal. The area may weep a little and form a crust which is normal.


It is a good habit to adopt a regime of sensible sun protection post treatment and long term. This should include avoiding the sun, wearing protective clothing and using sunscreens on all sun exposed parts of your skin (SPF 30+ on your face, neck and hands etc.)

Your PDT may need to be repeated after approximately 1 week depending on the type of lesion. Your doctor may want to see you again in around 3 months to review the outcome and advise whether any further treatment is necessary.

What are the potential side effects of photodynamic therapy?

The short term side effects of PDT include:

  • Pain - pain tends to be more significant in those patients treated with lamp PDT. When the red light is shone onto the skin, the treated area may hurt. If it is too uncomfortable the light intensity can be decreased or additional air cooling applied. After completion of treatment, discomfort and itching may last a few days and may require pain relief. With daylight PDT, patients may experience some mild stinging or tingling during treatment but rarely enough discomfort to stop treatment.

  • Inflammation - the treated area may become swollen or puffy and may ooze clear fluid a little, this is a normal reaction and should settle within a few days.

  • Blistering and ulceration - the treated area may occasionally blister or ulcerate.

  • infection - there is risk of infection due to the broken skin barrier. If the surrounding area becomes increasingly red, swollen and painful, an infection may have developed, and your should contact your doctor or nurse.

Potential long term side effects include:

  • Scarring - there may be some scarring after PDT but this is rare. Usually the skin texture is improved.

  • Colour change - the skin may become darker of lighter after PDT.

  • Treatment may not be effective or the condition may come back again - if this happens you may be offered further PDT or an alternative treatment.