This treatment is commonly used in certain kinds of skin cancer and pre-cancer. A cream containing a semi-intelligent molecule is applied to the skin. The molecule binds to the abnormal cells after about 3 hours on the skin.
Activation of the molecule by an intense beam of light applied to the skin then kills the damaged skin cells. The patient therefore attends firstly for the cream application and secondly for the light treatment approximately 3 hours later.
Quite often the treatment is repeated twice two weeks apart.