The uniqueness of one’s hair lies in its color, texture, and thickness, often reflecting personal style and cultural identity. While genetics play a significant role in determining these characteristics, certain life events such as puberty, pregnancy, and chemotherapy can lead to changes in hair texture and thickness, as well as the appearance of gray hair.
Hair, primarily composed of keratin, an insoluble protein, grows from individual hair follicles deep within the skin. The formation of curly hair occurs due to both the asymmetry of the hair follicle and the keratin within the hair strand.
Curly hair follicles are asymmetrical, curved, and positioned at an angle to the skin surface. As a result, the hair develops kinks as it begins to grow. Additionally, the asymmetry of the follicle causes the keratin to bunch up on one side of the hair strand, resulting in a curl that is maintained throughout its growth.
On the other hand, straight hair is produced by symmetrical, round follicles that grow perpendicular to the skin surface.
Throughout life, our hair undergoes cycles of growth and loss. Hair follicles contain stem cells that multiply and develop into hair strands. The growth phase of head hair can last for several years, followed by a transitional phase where the hair ceases to grow for approximately two weeks. Subsequently, there is a resting phase lasting a few months, during which the hair naturally falls out before the follicle generates a new hair strand, repeating the cycle. The replacement of each hair on the scalp occurs every three to five years.
The shape of our hair is largely determined by genetics, exhibiting incomplete dominance. Incomplete dominance refers to the existence of a middle version of a trait. In the case of hair, the presence of both curly hair and straight hair genes results in wavy hair. Hormonal changes during puberty and pregnancy can impact gene function, causing the activation of the curly hair gene in individuals with wavy hair. Consequently, their hair may change from wavy to curly.
Research has also shown that certain genes can be activated to alter hair shape in animals such as pigs, transforming straight hair to curly.
Chemotherapy is notorious for its visible effects on hair. The treatment targets rapidly dividing cells, including hair follicles, leading to hair loss. Moreover, chemotherapy can influence the genetic structure of hair follicles, resulting in regrowth with a different shape during the initial cycles.
Thyroid hormones play a crucial role throughout life in keratin production. Insufficient levels of thyroid hormones can cause hair to become dry and brittle. Additionally, estrogen and androgens influence hair growth and loss, particularly as individuals age.
Male pattern baldness, characterized by balding in males, stems from heightened androgen levels. Specifically, elevated dihydrotestosterone (DHT), derived from testosterone, contributes to this type of hair loss.
Female pattern hair loss occurs in some women due to a combination of genetic factors, reduced levels of estrogen, and increased androgens following menopause. Over time, the hair follicles become progressively smaller until they no longer produce hairs.
The graying of hair is attributed to diminished functionality of melanin-producing cells, resulting in reduced melanin production.
In conclusion, hormones and chemotherapy can induce significant transformations in hair texture, thickness, and color. By understanding the underlying science, we can appreciate the intricate processes that contribute to these changes and how they shape our hair throughout various stages of life.
