What is Human Hair Made Of?
Human hair is a complex biomaterial, not a simple protein filament. While keratin is the dominant component, the complete picture includes water, lipids, pigments, and trace elements. A single strand of hair consists of a shaft that extends above the skin and a root embedded in the hair follicle below the surface. The visible hair shaft itself has three main layers: the cuticle, cortex, and medulla. Each of these layers contributes to the hair's overall composition and characteristics.
The Role of Keratin
Keratin is a fibrous, structural protein that forms the core of the hair shaft. There are different types of keratin in the body, with specific "hard keratins" forming hair and nails, which are distinct from the softer keratins found in skin. This protein is particularly rich in the amino acid cysteine, which forms strong disulfide bonds that provide hair with its unique strength and stability. The arrangement and quantity of these bonds are what determine hair's shape and texture.
Beyond the Protein: Other Hair Components
Keratin is not the sole ingredient. Hair's composition also includes other vital elements:
- Water: Healthy hair contains an average of 10-15% water, which contributes to its flexibility and physical properties. Changes in humidity can significantly alter the hair's moisture level.
- Lipids: These fats and oils coat the hair, lubricating it and providing a protective barrier. Sebum, produced by sebaceous glands, is a major source of hair lipids that provide natural conditioning and shine.
- Melanin: This is the pigment responsible for hair color. Produced by melanocytes in the hair follicle, melanin is deposited into the hair shaft. The type and amount of melanin determine if hair is black, brown, red, or blonde. A decrease in melanin production over time is what causes hair to turn gray or white.
- Trace Elements: Hair contains small amounts of minerals like zinc, iron, copper, and calcium, which can be indicators of dietary or environmental exposure.
Hair Structure and Protein Content
Inside the hair shaft, the protein is organized within different layers. The central cortex makes up the bulk of the hair and contains the majority of the keratin. The outer cuticle layer, a series of overlapping cells, also contains keratin and serves as a protective shield for the inner cortex. The medulla, an innermost layer, is present only in some hair types and contributes additional structural support.
The Breakdown of Hair Protein
Over time, various factors can deplete the keratin in your hair, leading to damage. When the protein structure is compromised, the cuticle can lift and expose the vulnerable cortex, resulting in frizz, breakage, and dullness.
Common causes of keratin loss include:
- Chemical Treatments: Bleaching, coloring, and perms break the disulfide bonds in keratin to reshape the hair, causing significant damage.
- Excessive Heat Styling: High temperatures from tools like flat irons and blow dryers can alter the internal structures of hair, leading to protein loss.
- Environmental Factors: Exposure to UV radiation from the sun, pollution, and chlorinated water can weaken hair's protein structure.
- Poor Nutrition: As keratin is a protein, a diet lacking in sufficient protein, vitamins, and minerals can affect the body's ability to produce healthy hair.
- Over-washing: Using harsh shampoos or washing hair too frequently can strip away natural lipids that protect the keratin.
Comparison: Keratin vs. Other Components
| Component | Percentage of Hair (approximate) | Function in Hair | Impact on Hair Health |
|---|---|---|---|
| Protein (Keratin) | 65–95% | Provides structural strength, elasticity, and resilience. | High keratin = strong, resilient hair. Low keratin = weak, brittle hair. |
| Water | 10–15% | Adds flexibility and softness, affects physical properties. | Low water = dry, static hair. Balanced moisture = soft, flexible hair. |
| Lipids | 1–9% | Lubricates, moisturizes, and protects the hair and scalp. | Low lipids = dry, dull, and brittle hair. Healthy lipid balance = shiny hair. |
| Melanin | <1% | Determines hair color. | Provides natural pigmentation. Decrease in melanin leads to gray hair. |
| Trace Elements | <1% | Integral part of the hair fiber structure. | Reflects nutritional status and environmental exposure. |
Conclusion
To definitively answer the question "is human hair 90% protein?," the response is that it is a very common and scientifically-supported estimate, with some sources even suggesting percentages as high as 95%. The specific composition is a complex interplay of proteins, moisture, lipids, and pigments. The overwhelming majority of the hair shaft is indeed comprised of keratin, a fibrous protein that gives hair its strength. The remaining percentage consists of water, lipids that protect and lubricate, and melanin that provides color. While genetics determine much of your hair's inherent structure, lifestyle factors, diet, and proper hair care are crucial for maintaining the integrity of this protein and ensuring overall hair health.
For Further Reading
For a detailed biological overview of hair, including its structure, function, and growth cycle, consult reputable scientific sources like the National Center for Biotechnology Information (NCBI) bookshelf. A good starting point can be their article: Physiology, Hair - StatPearls - NCBI Bookshelf.
