Final answer:
The body switches from producing vellus hairs to terminal hairs during puberty due to hormonal changes. The hair growth cycle consists of anagen, catagen, and telogen phases, with hormones affecting both growth and loss of hair.
Step-by-step explanation:
The body naturally switches from producing vellus hairs, which are soft and fine, to terminal hairs, which are thicker, longer, and darker, during puberty. This process is influenced by hormonal changes, specifically an increase in androgens, which are sex hormones such as testosterone and dihydrotestosterone (DHT). Vellus hair can be found all over the body, whereas terminal hair forms in specific areas such as the scalp, underarms, and pubic region during puberty. The hair growth process involves the three phases of anagen, catagen, and telogen. Initially, babies are covered in a type of vellus hair called lanugo, which is shed before or shortly after birth. The transformation to terminal hair during puberty signifies sexual maturation and is part of the body's development.
Hair growth and loss are natural cycles controlled by the phases of anagen, catagen, and telogen, with hair growing at 0.3 mm per day during the anagen phase. Hormones can influence both hair growth and loss, with variations in hormone levels potentially leading to more hair being shed than is replaced, resulting in hair loss. The hormonal shifts during different life stages, including puberty, the aging process, and other hormonal influences lead to changes in hair type and density.