Hair texture is a complex biological trait, with hormones playing a dynamic role in its appearance throughout life. This article explores what causes hair to curl and the role hormones play.
The Science of Hair Curl
Hair curl begins with the hair follicle. The shape of the hair follicle is a primary determinant of whether hair grows straight, wavy, or curly. A perfectly round follicle typically produces straight hair, while an oval or elliptical follicle results in wavy or curly hair. The flatter the oval, the more pronounced the curl. The angle at which the follicle emerges from the scalp also influences curvature; straight hair follicles tunnel vertically, whereas curly hair follicles angle into the skin, causing the hair to curve as it grows.
Beyond the follicle’s shape, the internal structure of the hair shaft, primarily composed of keratin, plays a significant role. Keratin contains amino acids, notably cysteine, which form strong chemical bonds called disulfide bonds. Curly hair typically possesses more of these bonds than straight hair. These bonds contribute to the hair’s ability to bend and maintain its curled shape. Chemical treatments, such as perms or relaxers, work by altering these disulfide bonds to change hair structure.
Hormones That Influence Hair Texture
Hormones serve as chemical messengers that significantly impact various bodily functions, including hair growth and texture. Several key hormones influence the hair follicle and overall hair production. Androgens, such as testosterone and dihydrotestosterone (DHT), are male sex hormones present in both sexes. While androgens stimulate terminal hair growth in areas like the face and body during puberty, they can paradoxically lead to scalp hair thinning and loss in individuals genetically predisposed to androgenetic alopecia. High levels of androgens in women can contribute to scalp hair thinning and excessive facial or body hair.
Estrogens, the primary female sex hormones, generally promote hair growth and contribute to thicker, fuller hair. Estrogen achieves this by extending the anagen, or active growth, phase of the hair cycle. Higher estrogen levels are often associated with softer, shinier, and more manageable hair. Some observations suggest estrogen may influence curl patterns, with elevated levels potentially leading to looser or wavier curls.
Thyroid hormones, including thyroxine and triiodothyronine, are essential for regulating metabolism and keratin production, a main component of hair. Imbalances in these hormones can significantly affect hair texture and density. Hypothyroidism, an underactive thyroid, often results in dry, coarse, brittle hair and can lead to hair loss. Hyperthyroidism, an overactive thyroid, may cause hair to become thinned, brittle, or greasy, and can also contribute to shedding. Insulin, a hormone produced by the pancreas, can also impact hair texture and growth; imbalances may contribute to hair loss or alter hair’s appearance.
How Hormonal Shifts Affect Hair Curl
Significant hormonal shifts throughout life can lead to noticeable alterations in hair curl or overall texture. Puberty is a period marked by substantial hormonal changes, and for some, this can trigger a shift in hair texture. The surge in hormones, particularly estrogen in females, can physically change the shape of hair follicles, potentially causing previously straight hair to develop a wavy or curly pattern. This period can also bring increased oiliness due to stimulated sebaceous glands.
Pregnancy is another time of profound hormonal fluctuation, with increased estrogen levels often leading to thicker, more lustrous hair by prolonging the hair growth phase. After childbirth, a sharp drop in estrogen levels can result in significant hair shedding, a common occurrence known as postpartum hair loss. This hormonal adjustment can also manifest as changes in hair texture, such as increased dryness, frizz, or even a different curl pattern.
Menopause involves a substantial decline in estrogen and progesterone, along with a relative increase in androgen dominance. These hormonal changes can cause hair to become thinner, drier, and more brittle. Some individuals may also experience alterations in their curl pattern or overall hair texture during this stage of life.
Medical conditions also demonstrate the impact of hormonal imbalances on hair. Thyroid disorders can lead to changes in hair texture and density. Polycystic Ovary Syndrome (PCOS), characterized by elevated androgen levels, can result in scalp hair thinning. Even chemotherapy, by affecting hair follicles, can cause hair to regrow with a different texture.
Hormones and Genetics: Understanding the Full Picture
While hormones clearly influence hair texture, genetics remain the primary determinant of an individual’s baseline hair type. Genetic factors provide the fundamental blueprint for the shape of hair follicles and the structure of keratin proteins within the hair shaft. The specific genes inherited dictate whether the hair follicle will be round, oval, or elliptical, setting the foundational curl pattern.
Hormones, rather than being the sole cause of curly hair, act as modulators that can modify this genetically determined texture. Hormonal changes can activate or deactivate certain genes, leading to shifts in hair texture throughout a person’s life. While a person’s fundamental genetic predisposition for hair type is set, hormonal fluctuations can cause temporary or long-term changes in its expression, altering curl pattern, thickness, or overall texture.