Learn about the three types of hair the human body grows, as well as the phases of hair growth.
Introduction to Human Hair Types
Hair is a complex and fascinating part of our biology as human beings, serving various functions from protective to esthetic. To fully understand the growth phases of human hair, it is essential first to familiarize yourself with the three primary types of hair that our bodies produce: lanugo, vellus, and terminal hair. Each type differs significantly in terms of location, characteristics, and role within the human body.
Lanugo Hair: The First Type
Lanugo hair represents the earliest stage of human hair development. This fine, soft hair begins to cover the body of a fetus around the fourth or fifth month of pregnancy. Lanugo serves multiple crucial functions, primarily providing warmth and protection to the developing fetus. The delicate hairs form a protective layer, helping to regulate the fetus’s temperature within the amniotic fluid. Additionally, lanugo plays a key role in safeguarding the fetus’s sensitive skin by preventing friction and potential damage from the amniotic sac.
Lanugo hair typically falls out before the baby is born, usually in the seventh or eighth month of pregnancy. Vellus hair grows in to cover the body after birth, replacing the lanugo that fell out. But some babies, particularly those who are born early, may still retain lanugo hair when they are born. This residual lanugo generally disappears within a few weeks as the infant’s skin adapts to the external environment.
Vellus Hair: The Body’s Peach Fuzz
Vellus hair, aka “peach fuzz,” is a fine, light hair texture that most people have. If you’re comparing it to terminal hair — the thicker, darker hair on your scalp, eyebrows, and other parts — you’ll notice that it’s thinner and lighter in color. Vellus hair is softer and less pigmented than terminal hair because it does not have the medulla, the innermost component of the hair shaft.
Vellus hair’s main purpose is to provide a layer of insulation and help us maintain a constant body temperature. This type of hair helps to trap air close to the skin, reducing heat loss. Additionally, vellus hair plays a role in sensory perception by enhancing the skin’s sensitivity to light touch and external stimuli.
As puberty sets in, hormonal changes cause some vellus hairs to turn into terminal hairs. A guy’s chest, face, and other areas of the body become covered in more terminal hair when his androgen levels are high. In females, hormonal changes can lead to the development of terminal hair in the pubic and underarm regions. However, the extent and pattern of this transformation vary widely among individuals and are influenced by genetic factors.
Vellus hair can also change in response to hormonal fluctuations throughout a person’s life. Conditions such as polycystic ovary syndrome (PCOS) can cause an increase in androgens, leading to the conversion of vellus hair into terminal hair in areas not typically associated with significant hair growth. Conversely, a decrease in hormone levels, such as during menopause, may result in thinning.
Terminal Hair: The Mature Hair Type
Terminal hair represents the mature form of human hair that typically emerges during and after puberty. This type of hair is characterized by its thickness, pigmentation, and often coarser texture compared to other hair types. Terminal hair is primarily found on the scalp, face, underarms, and other parts of the body, including the chest and pubic areas. Terminal hair is the hair type that is most often removed during waxing.
Genetics play a significant role in determining the growth patterns, color, and texture of terminal hair. The hereditary traits inherited from one’s parents dictate the density and pigmentation of hair. Similarly, the texture of terminal hair, whether it is straight, wavy, or curly, is largely influenced by genetic factors.
Hormones, particularly androgens, are crucial in the development and maintenance of terminal hair. During puberty, the increase in androgen levels triggers the transformation of vellus hair into terminal hair. This hormonal influence is more pronounced in males, resulting in more substantial growth of facial and body hair compared to females.
The Phases of Hair Growth
The human hair growth cycle consists of three primary phases: anagen, catagen, and telogen.
Anagen is the most active period of hair growth. During this phase, cells in the hair root are rapidly dividing, adding to the hair shaft. This phase can last anywhere from two to seven years, depending on factors such as genetics, age, and overall health. Approximately 85% to 90% of hair follicles are in the anagen phase at any given time.
Catagen follows and is a brief transition lasting around two to three weeks. The hair follicle contracts and separates from the dermal papilla — the structure that supplies nutrients to the growing hair — and hair growth stops.
Telogen is the resting phase and lasts around three months. The follicle remains dormant and the fully formed hair is at rest. Eventually the hair is shed, making way for a new hair to begin growing in the anagen phase. Typically about 10% to 15% of follicles are in telogen at any time.
Factors Influencing Hair Growth and Health
Genetics. The hereditary pattern of hair growth, thickness, and color is passed down from generation to generation. Genetic predisposition can also contribute to conditions like androgenetic alopecia, commonly known as male or female pattern baldness.
Hormonal changes. Pregnancy, menopause, and thyroid imbalances can lead to noticeable changes in hair density and texture. During pregnancy, elevated levels of estrogen prolong the growth phase, resulting in thicker hair. Postpartum hormonal shifts can then lead to shedding.
Nutrition. Proteins, vitamins (A, C, D, and E), and minerals like iron and zinc all play significant roles in hair growth. Deficiencies can lead to thinning and loss. Leafy greens, nuts, seeds, and lean proteins support robust hair health.
Lifestyle. High levels of stress are associated with a temporary hair loss condition known as telogen effluvium. Adequate sleep and stress management can promote healthier hair, as can gentle hair care practices — avoiding excessive heat styling and using mild shampoos.
Understanding the factors that influence hair growth and health is essential for effective hair care. By acknowledging the roles of genetics, hormonal changes, nutrition, and lifestyle, you can adopt strategies to support stronger, healthier hair.