What type of keratin is found in the fingernails and hair?

The type of keratin found in fingernails and hair is hard keratin. Hard keratin is particularly durable and resistant to wear, which is essential for structures like hair and nails that endure frequent physical stress and environmental exposure. This toughness is due to the high sulfur content in hard keratin, which forms strong disulfide bonds between keratin fibers, making it less flexible but significantly more resilient compared to other types of keratin.

Soft keratin, on the other hand, is found in areas such as the skin and is more pliable and less dense, which suits the skin's need for flexibility and resilience but isn't suitable for nails or hair. Elastic keratin is not a standard classification of keratin associated with hair or nails, as its properties would not align with the structural demands of those tissues. Lastly, collagen is not a type of keratin; it is a separate protein primarily found in connective tissues, providing strength and elasticity to skin and other structures.