"How Does the Sun Damage Your Hair? Keratinocytes in your skin synthesize vitamin D to produce keratin – the protein that keeps your hair and skin healthy. Keratin forms a protective covering for your hair shaft. Yes, vitamin D deficiency means weakened hair cuticles and stunted hair growth. However, too much sun can break into the protective keratin layer, leaving the hair shaft bar... https://www.joskinrevive.com/effect-of-summer-sun-on-hair/