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Photodynamic therapy (PDT) is a treatment that involves the use of light-sensitive medication and a light source to destroy abnormal cells.
It can be used to treat some skin and eye conditions, as well as certain types of cancer.
On their own, the medication and light source are harmless, but when the medication is exposed to the light, it activates and causes a reaction that damages nearby cells.
This allows small abnormal areas of tissue to be treated without the need for surgery.
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PDT can be used to treat abnormal cells in parts of the body a light source can reach, such as the skin, eyes, mouth, oesophagus (gullet) and lungs.
Conditions sometimes treated with PDT include:
PDT is carried out in two stages.
If your skin was treated, it'll be covered by a dressing that should remain in place for about a day. Your care team will tell you exactly how long.
Try to avoid scratching or knocking the treated area, and keep it as dry as possible.
Once you're advised to remove the dressing, you can wash and bathe as normal, as long as you gently pat the treated area dry.
A follow-up appointment at the hospital or clinic will be arranged to assess whether the treatment has been effective and decide if it needs to be repeated.
It usually takes around two to six weeks for the area to heal completely, depending on which part of the body has been treated and how big the area is.
PDT is a very safe treatment, although the following side effects are common:
Other potential side effects depend on the area treated.
Talk to your doctors about the possible risks of PDT before having the treatment.
PDT as described above is an effective and licensed treatment for a number of conditions.
It shouldn't be confused with the unproven, unlicensed versions sold by some private clinics in the UK and overseas.
Clinics promoting these so-called "advanced" versions of PDT, called "next-generation PDT" (NGPDT) and "sonodynamic therapy" (SDT) sometimes claim they can treat deep or widespread cancers. But these claims are not supported by scientific evidence and these treatments aren't recommended, even as a last resort.