[Historical development of photodynamic therapy]

Photodynamic therapy is based on the accumulation of photosensitizing drugs in tumours and subsequent activation by visible light, leading to the release of singlet oxygen in photochemical reactions. Besides the treatment of precancerous lesions and malignant tumours in superficial sites, new experimental indications, such as psoriasis, are being investigated. The development of new photosensitizing agents for topical application and appropriate light sources has led to increasing interest in this promising treatment modality among dermatologists. This historical review deals with the scientific investigations of photodynamic therapy and diagnosis that started with the experiments of Oscar Raab at the end of the nineteenth century.