Hair and nails, despite their distinct appearances, share a fundamental component. Both structures are integral to the integumentary system. While hair is flexible and nails are rigid, their underlying biological makeup reveals a surprising connection.
The Shared Component: Keratin
Both hair and nails are primarily composed of a fibrous structural protein known as keratin. This protein is a fundamental building block found in hair, nails, and the outer layer of the skin. Keratin provides support and protection, contributing to the strength and health of these tissues. The human body produces keratin, with many different types present.
Keratin’s structure forms strong, insoluble fibers, making hair and nails tough and strong.
Structural Differences and Characteristics
Despite sharing keratin, hair and nails exhibit significant structural differences. The primary type of keratin found in both is alpha-keratin. The arrangement and chemical bonds within this keratin differ substantially. In hair, alpha-keratin forms a coiled-coil structure, which contributes to its flexibility. Hair also contains hydrogen bonds, which are easily broken by water, allowing for temporary changes in hair shape.
Nails, on the other hand, contain a harder form of keratin, often described as beta-keratin-like. This increased hardness is due to a higher concentration of sulfur, leading to a greater number of disulfide bonds. These strong disulfide bonds create a more rigid and stable structure in nails, making them less flexible than hair. Water content also varies; hair typically has a higher water content, around 15-25%, which contributes to its pliability, while nails have a lower water content, approximately 12-18%, further enhancing their hardness.
How They Form and Grow
Hair and nails both originate from specialized areas of living cells that continuously produce the keratinized material. Hair growth begins within the hair follicle, embedded in the skin’s dermis. Cells at the follicle’s base multiply, and as they are pushed upward, away from their nutrient supply, they fill with keratin and die, forming the visible hair shaft. Each hair follicle contains stem cells for continuous hair growth.
Nails grow from the nail matrix, an active tissue at the base of the nail, under the cuticle. The nail matrix generates new nail cells, which harden and keratinize as they are pushed forward. As new cells form, they compress older cells, creating the visible nail plate. Both hair and nails are composed of these dead, keratin-filled cells, which is why cutting them does not cause pain. This continuous production allows for their constant growth.