Human hair is one of the most fascinating and versatile parts of our body. It can express our personality, mood, and style, as well as protect us from the sun, cold, and injury. But how much do we really know about our hair? What is it made of, how does it grow, and what factors affect its health and appearance? In this article, we will answer these and other common questions about human hair, and provide you with some useful tips and recommendations for keeping your hair strong, shiny, and beautiful.
What is human hair and where does it come from?
Human hair is a protein filament that grows from hair follicles in the skin. Hair follicles are tiny organs that produce hair cells and secrete oils and sweat. Hair cells are made of keratin, a type of protein that also forms our nails, skin, and some animal parts, such as horns, hooves, and feathers. Keratin gives hair its strength, elasticity, and resistance to damage.
Human hair comes in different colors, textures, and patterns, depending on our genetics, ethnicity, and environment. The color of our hair is determined by the amount and type of pigment (melanin) in our hair cells. The texture and pattern of our hair are influenced by the shape and size of our hair follicles and the angle at which they emerge from the skin. For example, round follicles produce straight hair, while oval follicles produce wavy or curly hair.
The medulla is the innermost layer of the hair shaft, composed of moderately keratinized cells that serve as the pith or marrow of the hair. Not all human hairs have a medulla. The medulla is typically found in thicker hairs, such as terminal hairs that grow on the scalp, eyebrows, eyelashes, and body. However, it is often missing or discontinuous in finer hairs, such as vellus hairs that cover most of the skin. The presence or absence of the medulla can help identify the type and origin of a hair sample.
How many hair follicles do we have and how do they change over time?
The average human has about 90,000 to 150,000 hair follicles on their head, and about 5 million hair follicles on their entire body. However, this number can vary depending on the individual’s hair color, density, and genetics. For instance, natural blondes tend to have more hair follicles than brunettes or redheads, while people of Asian descent tend to have fewer but thicker hair follicles than people of European or African descent.
The number of hairs on the human head can vary by individual, hair color, and hair density. However, the average person has about 100,000 hairs on their head, with a similar number of hair follicles.
The average hair density is between 800 to 1,290 hairs per square inch (124 to 200 hairs per square centimeter). However, people with thick hair may have higher hair density than the average. Thick hair is usually defined as having a large diameter or circumference of each hair strand, which can range from 0.04 to 0.05 mm.
People with thick hair may have more hair follicles than people with thin or fine hair, or they may have larger or more active hair follicles that produce thicker hair strands. The number of hairs on a human head with thick hair can also depend on other factors, such as genetics, ethnicity, age, and health. Some estimates suggest that people with thick hair may have up to 150,000 hairs on their head, but this number can vary widely.
We are born with all the hair follicles we will ever have, and they do not regenerate or increase in number. However, they can change in size, shape, and activity over time, due to factors such as aging, hormones, stress, diet, medication, disease, and hair loss. As we age, our hair follicles tend to shrink and produce thinner, shorter, and less pigmented hair, resulting in grey hair and baldness.
Hormones, such as testosterone and estrogen, can also affect the growth and distribution of our hair, especially during puberty, pregnancy, and menopause. Stress, diet, medication, disease, and hair loss can also alter the function and health of our hair follicles, causing them to produce less or no hair, or to become inflamed or infected.
It is normal to lose some hair every day as part of the natural hair growth cycle. The average person loses between 50 and 100 hairs per day, but this number can vary depending on the individual’s age, genetics, health, nutrition, and hair care. Hair loss can also increase temporarily due to factors such as stress, illness, medication, or hormonal changes.
Hair loss is different from hair shedding, which is when the hair strand falls out at the end of its resting phase. Hair loss is when the hair follicle stops producing new hair cells, leading to thinning or balding. Hair loss can be caused by various conditions, such as alopecia, thyroid disorders, autoimmune diseases, or scalp infections.
How fast does human hair grow and what are the stages of its growth cycle?
Human hair grows at an average rate of 0.5 inches (1.25 cm) per month, or 6 inches (15 cm) per year. However, this rate can vary depending on the individual’s age, genetics, health, nutrition, and hair care. For example, hair tends to grow faster in young adults, women, summer, and healthy people, while it tends to grow slower in older adults, men, winter, and unhealthy people.
Human hair grows in a cyclic pattern, consisting of three main phases: anagen, catagen, and telogen. These phases determine the length, thickness, and lifespan of each hair strand.
- Anagen is the active growth phase, during which the hair follicle produces new hair cells and pushes them upward. This phase lasts from 2 to 8 years, depending on the individual and the body part. About 85 to 90% of the hair on our head is in the anagen phase at any given time.
- Catagen is the transition phase, during which the hair follicle shrinks and detaches from the blood supply. This phase lasts for about 2 to 4 weeks, and marks the end of the growth phase. About 1 to 2% of the hair on our head is in the catagen phase at any given time.
- Telogen is the resting phase, during which the hair follicle remains dormant and the hair shaft falls out. This phase lasts for about 2 to 4 months, and prepares the hair follicle for the next growth cycle. About 10 to 15% of the hair on our head is in the telogen phase at any given time.
How strong is human hair and what are the factors that affect its strength?
Human hair is surprisingly strong, considering its thin and flexible nature. A single strand of hair can withstand a tensile force of about 3.5 ounces (100 grams), or the weight of two candy bars. A full head of hair can support up to 12 tons (24,000 pounds), or the weight of two elephants. However, this does not mean that we should use our hair as a rope or a crane, as it can still break or tear under excessive stress or friction.
The strength of our hair depends on several factors, such as its diameter, structure, moisture, and condition. The diameter of our hair varies from 0.016 to 0.05 mm, depending on the individual and the hair type. Thicker hair tends to be stronger than thinner hair, as it has more keratin and cross-links.
The structure of our hair consists of three layers: the cuticle, the cortex, and the medulla. The cuticle is the outermost layer, made of overlapping scales that protect the inner layers. The cortex is the middle layer, made of long and twisted fibers that give the hair its strength, elasticity, and color. The medulla is the innermost layer, made of soft and hollow cells that provide insulation and buoyancy. The strength of our hair depends on the integrity and alignment of these layers, as well as the bonds between them.
The moisture of our hair affects its flexibility and resilience, as it allows the hair to stretch and bend without breaking. The condition of our hair reflects its health and damage, as it influences its smoothness, shine, and resistance to breakage. Healthy hair has a smooth and intact cuticle, a strong and elastic cortex, and a well-hydrated and nourished medulla. Damaged hair has a rough and lifted cuticle, a weak and brittle cortex, and a dry and hollow medulla.
How many hairs do we have and how much do they weigh?
The number of hairs we have depends on the number of hair follicles we have, which varies from person to person and from body part to body part. As we mentioned before, the average human has about 90,000 to 150,000 hair follicles on their head, and about 5 million hair follicles on their entire body. However, not all hair follicles are active or visible, as some may be dormant, miniaturized, or vellus (fine and unpigmented). Therefore, the number of hairs we have is usually lower than the number of hair follicles we have.
The weight of our hair depends on the length, thickness, and density of our hair, as well as the moisture and oil content. The average human head weighs about 10 to 11 pounds (4.5 to 5 kg), and the hair accounts