Human Hair and Scalp: Structure, Loss, Conditions

Author: Disabled World (DW)
Updated/Revised Date: 4 Aug 2026

Table of Contents:
Synopsis - Definition - About This Section - FAQs - Publications - Subtopics

Synopsis

Learn how human hair grows from the follicle, what causes dandruff, gray hair, and baldness, plus the structure, texture, and treatments behind hair loss today.

At a Glance

• 1 - Human facial hair grows faster than any other hair on the body.
• 2 - Scalp hair grows at 0.4 mm a day, four times the rate of human nails.
• 3 - Red hair usually does not turn gray; it fades to a sandy shade and then to white.
• 4 - Gray hair develops as hydrogen peroxide builds up in the follicles from ordinary wear, and nearly everyone aged 75 or older has it.

Topic Definition

Human Hair

Human hair is a protein filament, made largely of keratin, that grows up through the epidermis from a follicle rooted deep in the dermis. Along its length each hair has a bulb at the base, a root hidden beneath the skin, and a shaft that rises above the surface, while a cross-section reveals three layers: an outer cuticle of overlapping cells, a keratin-packed cortex, and a central medulla holding loose cells and air spaces. Hair grows almost everywhere on the body apart from areas such as the palms and soles, and only the portion inside the follicle is truly alive, since the visible strand has no biochemical activity and is considered dead. Its color, texture, and growth are shaped by genetics, aging, hormones, and health, which is why changes in hair are often noticed as a person grows older or unwell.

Overview

Defining Human Hair

Hair is defined as a protein filament that grows through the epidermis from follicles deep within the dermis. Hair can grow on most areas of the human body, except on the palms of the hands and the soles of the feet (among other areas), but hair is most noticeable in most people in some areas, which are also the ones that are most commonly trimmed, plucked, or shaved. These include the face, nose, ears, head, eyebrows, eyelashes, legs and armpits, as well as the pubic region.

The most common interest in hair is focused on hair growth, hair types and hair care, but hair is also an important biomaterial primarily composed of protein, notably keratin.

Hair can be divided into three parts length-wise:

• (a) the bulb, a swelling at the hair base which originates from the dermis.
• (b) the root, which is the hair lying beneath the skin surface.
• (c) the shaft, which is the hair above the skin surface.

In cross-section, there are also three parts:

• (a) the medulla, an area in the core which contains loose cells and air spaces
• (b) the cortex, which contains densely packed keratin
• (c) the cuticle, which is a single layer of cells arranged like roof shingles.

Human scalp hair normally grows at 0.4 mm /day (incidentally, human scalp hair grows at a rate four times that of human nails. Human nails grow at 0.1 mm/day). It is commonly accepted that emotional distress, especially that caused by verbal abuse, etc. often is a contributing factor to a slower hair growth rate.

Dandruff

Dandruff is due to excessive shedding of dead skin cells from the scalp, and can also be caused by frequent exposure to extreme heat and cold. As it is normal for skin cells to die and flake off, a small amount of flaking is normal and in fact quite common. Some people, however, either chronically or as a result of certain triggers, experience an unusually large amount of flaking, which can also be accompanied by redness and irritation.

Hair Texture

Usually defined as fine, medium, coarse, wiry or frizzy hair depending on the hair diameter.

Within these four texture ranges hair can also be thin, medium or thick density, and it can be straight, curly, 'kinky' (tightly coiled), or wavy.

Hair conditioner also affects hair texture. Hair can be healthy, normal, oily, dry, damaged or a combination. Hair texture can also be impacted by hairstyling equipment such as straighteners, crimper's, or curlers.

Curly or 'kinky' hair has a different biological structure from straight hair. It tends to be much drier than straight hair because the oils secreted into the hair shaft by the sebaceous glands can more easily travel down the shaft of straight hair. People with very curly hair may find that this hair type can be dry and often frizzy.

Gray Hair

Gray hair is considered to be a characteristic of normal aging.

The tendency of older people to develop gray hair is due to a build up of hydrogen peroxide due to wear and tear of the hair follicles. The age at which this occurs varies from person to person, but in general nearly everyone 75 years or older has gray hair, and in general men tend to become gray at younger ages than women.

Red hair usually doesn't turn gray with age; rather, it becomes a sandy color and afterward turns white.

Hair Loss

Often drugs used in cancer chemotherapy will frequently cause a temporary loss of hair, most noticeable on the head and eyebrows because they kill all rapidly dividing cells, not just the cancerous ones.

Other diseases and traumas can cause temporary or permanent loss of hair, either generally or in patches. Patients with Hyperthyroidism or Hypothyroidism can experience hair loss until their hormone levels are regulated.

Baldness

Involves the state of lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia. The amount and patterns of baldness can vary greatly; it ranges from male and female pattern alopecia (androgenic alopecia, also called androgenetic alopecia or alopecia androgenetica), alopecia areata, which involves the loss of some hair from the head, and alopecia totalis, which involves the loss of all head hair, to the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.

Treatments for various forms of alopecia have limited success. Some hair loss sufferers make use of clinically proven treatments such as finasteride and topically applied minoxidil in an attempt to prevent further loss and regrow hair. As a general rule, it is easier to maintain remaining hair than it is to regrow; however, the treatments mentioned may prevent hair loss from Androgenetic alopecia, and there are new technologies in cosmetic transplant surgery and hair replacement systems that can be completely undetectable.

In the USA, there are only two drug-based treatments that have been approved by the U.S. Food and Drug Administration (FDA) and one product that has been cleared by the FDA for the treatment of androgenetic alopecia, they are finasteride (marketed for hair loss as Propecia) and minoxidil.

When Will I Go Bald? Find Out with Our Hair Loss Calculator.

Facts and Statistics About Hair

• Hair grows with about 1 cm every month.
• Hair is made mostly of a protein called keratin.
• Human facial hair grows faster than any other hair on the body.
• On average, we lose 50 to 100 strands of hair a day from the scalp.
• Human hair grows faster in warm weather because it stimulates hair growth.
• Cutting your hair does not affect in any way the rate of hair growth, nor its texture.
• The person on average has up to 100,000 to 150,000 hair strands on his or her head.
• There are two main types of hair that the body produces, vellus hair and terminal (or androgenic) hair.
• Hair fibers, or strands, grow from an organ in the area under the skin called a follicle, which is found in the dermis skin layer.
• The only "living" part of a hair is found in the follicle as it grows. The hair strand above the skin has no biochemical activity and so is considered "dead".
• On average, the lifespan of a human hair is 2 to 7 years. The hair on our scalp goes through 3 phases, the anagen phase, catagen phase, and telogen phase.
• The cross-section of a hair strand is made up of 3 key layers. The outer layer is called the cuticle, within that is the cortex (which contains the keratin), while the center layer is called the medulla.
• Goose bumps which form on skin when the body is cold are created when muscles attached to hair follicles stand up, which causes hair in these follicles to also stand, creating a heat-trapping layer in the skin.

Frequently Asked Questions

How often should I wash my hair

Washing frequency depends on hair type and oil production, with oily hair often needing more frequent washing and dry or curly hair benefiting from washing less often to keep natural oils.

Does stress cause hair loss

Emotional distress can contribute to a slower growth rate and, in some cases, temporary shedding, though hair usually recovers once the underlying stress is managed.

Can dandruff be cured permanently

Dandruff can usually be controlled rather than permanently cured, and medicated shampoos along with a steady scalp care routine help keep flaking and irritation in check.

Is gray hair reversible

Gray hair from natural aging is generally not reversible, since it results from changes within the follicle, though some causes linked to nutrition or illness may improve when treated.

What is the difference between vellus and terminal hair

Vellus hair is the fine, soft, lightly colored hair that covers much of the body, while terminal hair is the thicker, longer, pigmented hair found on the scalp, face, and other areas.

Does wearing hats cause baldness

Wearing hats does not cause baldness, as common hair loss is driven mainly by genetics and hormones rather than by anything worn on the head.

How much hair loss per day is normal

Losing about 50 to 100 strands from the scalp each day is considered normal, and this everyday shedding is part of the natural hair growth cycle.

Curated and edited by Ian C. Langtree, Founder & Editor-in-Chief, Disabled World. This section is maintained by the Disabled World editorial team.

Last updated: 4 Aug 2026