How could diet affect skin, hair, and nails?

The integumentary system is complex and requires many nutrients to function correctly. As such, a diet that provides adequate levels of nutrients — notably, protein, certain micronutrients (e.g, cysteine, lysine, iron, vitamin A, vitamin C, B vitamins, zinc, selenium), and essential fatty acids such as omega-6 and omega-3 polyunsaturated fatty acids — is important.^[1] Not only are these nutrients necessary for ordinary function, but they also play a role in protection and repair (e.g., in response to UV radiation). Deficiencies in these nutrients may manifest as abnormalities in skin, hair, and nails.^[2][3]