KRT1 and acne: Confirming the in vitro results, ALA-PDT showed significant effects of reducing K1, K6, and K16 that reflecting similar efficacy in vitro, as well confirming the previous study on histology of human skin samples which concluded that one of the mechanisms of ALA-PDT in acne treatment was reducing follicular obstruction by changing keratinocyte shedding and hyperkeratosis2.