Hair

Hair grows from small holes in your skin.

These holes are called follicles. The follicle is the only living part. It makes the hair grow.

The part you see is the hair shaft. It is made of dead cells. This part is very strong.

Tiny bits of color live inside your hair. These bits are called melanin. They make hair black, brown, or red.

Your hair can be straight or curly. The shape of the hole changes this. Round holes make straight hair. Oval holes make curly hair.

Hair is a part of many animals. We call these animals mammals.

Most hair grows from small holes in the skin. These holes are called follicles. The follicle is the only living part of the hair. It stays under the skin. Inside the follicle, cells make the hair grow.

The part you see is the hair shaft. It is made of a protein called keratin. This protein makes the hair strong. The shaft is actually made of dead cells.

Tiny bits of color live inside the hair. These bits are called melanin. They give hair its color. Eumelanin makes hair brown or black. Pheomelanin makes hair red.

Your hair shape depends on the follicle. Round follicles make straight hair. Oval follicles make wavy or curly hair.

Hair grows at different speeds. On average, it grows about 1 cm each month. Some scalp hair grows even faster. Hair growth stops after a person dies.

Hair is a special part of many living things. It is one of the main things that makes an animal a mammal.

Most hair grows from tiny holes in the skin called follicles. These follicles are found in a layer of skin called the dermis. The hair you can see is called the hair shaft. This part is made of dead cells that are very strong. They are held together by a protein called alpha-keratin.

How does hair actually grow? It all starts deep inside the hair follicle. The only living part of a hair is found in the follicle. At the very bottom is the hair bulb, which is soft and white. Inside this bulb, cells work to create the hair shaft. As the shaft grows, it pushes up through the skin. The hair shaft has three main layers. The outside layer is the cuticle, which looks like overlapping roof shingles.

The middle layer is the cortex, which gives the hair strength. The very center is called the medulla, which is an open area.

People have used hair to show who they are for a long time. In many cultures, hairstyles can show a person's age or religion. Hair can even show a person's social position. Different groups of people have different types of hair. For example, people with mostly African ancestry often have hair with a diameter of 60 to 90 micrometers. People with mostly Asian or Native American ancestry often have hair that is 90 to 120 micrometers wide.

Color comes from tiny bits of pigment called melanin. These granules are packed into the hair fibers inside the follicle. There are two main types of melanin. Eumelanin is the pigment that makes hair brown or black. Pheomelanin is the pigment that makes hair red.

If a person has very little pigment, they may have blond hair. Gray hair happens when melanin production slows down or stops. A person might even have white hair in certain spots called poliosis.

Your hair shape depends on the shape of your follicle. Round follicles create straight hair. Oval follicles make the hair look wavy or curly.

There is a famous way to group hair called the Andre Walker system. This system uses four types: straight, wavy, curly, and kinky. Type 1 is straight hair and is often very shiny. Type 4 is kinky hair, which has a very tight coil. Hair grows at different speeds for everyone. On average, hair grows about 1 centimeter every month.

Hair is a protein filament that grows from follicles located in the dermis, a layer of skin. It is one of the defining biological characteristics of mammals. Most human skin is covered in follicles that produce different types of hair, such as thick terminal hair or fine vellus hair. While many people focus on hair care or styles, hair is actually a vital biomaterial. It is primarily composed of a protein known as alpha-keratin.

To understand hair, we must distinguish between its two main structures. The hair follicle is the part located beneath the skin. It contains stem cells that can regrow hair after it falls out. These stem cells can also help regrow skin after a wound. The hair shaft is the hard, visible part that extends above the skin surface. The shaft is made of multi-layered, keratinized dead cells. These cells form rope-like filaments that provide strength and structure.

The hair shaft is organized into three distinct zones. The outermost layer is the cuticle, which consists of thin, flat cells that overlap like roof shingles. This structure slides as the hair swells. A single molecular layer of lipid covers the cuticle to help the hair repel water. The middle layer is the cortex, which is the primary source of mechanical strength and water uptake. The cortex also contains melanin, the pigment that colors the hair. The innermost region is the medulla, which is an open and disorganized area. The medulla is not always present in every hair fiber.

Hair color is determined by the distribution of melanin granules within the cortex. There are two main types of these pigments. Eumelanin is the dominant pigment found in black and brown hair. Pheomelanin is the pigment that makes red hair appear. Blond hair results from having very little pigmentation in the strand. As people age, melanin production may decrease or stop, resulting in gray hair. A condition called poliosis can cause white hair to appear in specific spots.

Growth is a continuous cycle involving three specific phases: anagen, catagen, and telogen. Each individual strand of hair is at a different stage of this cycle at any given time. Growth begins inside the follicle, which is the only living portion of the hair. The base of the root is called the bulb, and it contains the cells that produce the shaft. On average, hair grows about 1 centimeter per month. However, scalp hair growth can vary between 0.6 cm and 3.36 cm per month.

Texture and curl patterns are closely linked to the shape of the hair follicle. A round follicle produces a round hair fiber, which results in straight hair. Oval or other shaped fibers result in wavy or curly hair. This happens because the shape affects how disulfide bonds are arranged. In straight hair, these bonds are in a direct line. In curlier hair, the flatter shape allows more cysteines to compact together, creating bends.

Many scientists use the Andre Walker Hair Typing System to classify hair into four categories. Type 1 is straight hair, which is often shiny and oily because sebum spreads easily along the shaft. Type 2 is wavy hair, which sits between straight and curly textures. Type 3 is curly hair that often forms an S-shape. Type 4 is kinky hair, which features a very tight coil and high density. This type is often fragile because it has fewer cuticle layers.

Human hair characteristics also vary significantly by ancestry and diameter. The diameter of human hair ranges from 20 to 120 micrometers. People of African ancestry often have hair with a diameter of 60–90 μm and a flat cross-section. People of European or Middle Eastern ancestry often have a diameter of 70–100 μm and an oval cross-section. People of Asian or Native American ancestry often have a diameter of 90–120 μm and a round cross-section.