Keratin Keratin: a fibrous protein that makes up the structure of nails and hair.Related Articles: The Impact of Peel-Off Basecoats on Nail HealthMyth: External Application of Vitamins and Nutrients for Stronger, Healthier NailsCan Nail Oils Really Help Nails Grow Faster?Understanding Polymer-Based Nail HardenersWhat is Breathable Nail Polish?