sentences:  PDT has the most supporting evidence of all light therapy modalities.When regular light is used immediately following the application of a sensitizing substance to the skin such as aminolevulinic acid or methyl aminolevulinate, the treatment is referred to as photodynamic therapy (PDT).PDT treats acne by using various forms of light (e.g., blue light or red light) that preferentially target the pilosebaceous unit.