Historical clue formulations

• Skin layer — 2021-10-27
• It's only skin-deep — 2019-06-14
• Layer of skin — 2017-11-19
• Base of a follicle — 2016-02-27
• Skin layer — 2010-11-07
• Skin layer — 2010-04-27
• Skin layer — 1994-04-12