Yet, a functional role for the peripheral molecular clock in human HF physiology has only recently been identified: ex vivo, human HFs not only maintain circadian rhythmicity of core clock gene (CLOCK, BMAL1 and PER1) transcription in organ culture, but PER1 protein expression is also highly hair cycle dependent, increasing as HFs enter catagen [26]. This evidence concerns the gene BMAL1 and Hand-foot syndrome.