Photodynamic therapy (PDT) - also known as photochemotherapy - is used for the treatment of sunspots, superficial basal cell carcinoma and Bowen's disease.
It works by applying a photosensitising agent (in the form of a cream) to the lesion, which is absorbed by all the cells in the area where it is applied. This agent generally leaves healthy cells relatively quickly, but is retained by cancerous cells for a longer period.
When cancerous cells with the photosensitising agent still inside them are subjected to light of a specific wavelength they produce an active form of oxygen that kills these cells. It is also possible that the treatment helps to damage blood vessels in cancerous tumours and may also activate the body's own immune system to fight the cancer cells.
Before the photosensitising cream is applied the area of skin being treated is scraped gently. The cream must stay on for around three hours before a red wavelength light is shone on the affected area of skin for 7-8 minutes. The skin is then covered with a dressing for 24 hours to protect it from light. It is important that the affected area of skin is kept covered and dry.
There may be some pain associated with the treatment, especially if this is on areas of skin on the face. Pain can be relieved during the treatment in a number of ways such as cold water spray or a cold water pack, a fan blowing cold air at the face or if necessary a local anaesthetic.
Further treatment may be required within one to four weeks except where it is used to treat sunspots, where one treatment is all that is normally required.
PDT is effective in around 80-85% of cases.