Common misconception: shaving causes hair to grow back thicker and at a faster rate

Human hair growth is regulated by complex biological mechanisms that act primarily at the hair follicle, a structure located in the dermis. This follicle follows a hair cycle consisting of several successive phases. The longest phase is the anagen phase, or growth phase, which lasts from 2 to 7 years. During this period, cells divide rapidly at the base of the hair, while matrix cells migrate outward to form the hair shaft. Next comes the catagen phase, a short transitional phase of about three weeks, during which the follicle undergoes involution: the hair loses its connection with the papilla and retracts. The telogen phase, or resting phase, follows for about three months; it is a period of near-zero cellular proliferation, with the papilla retracting toward an area near the bulge, without significant apoptosis. Finally, there is a distinct phase called exogen, corresponding to the shedding of the old hair while a new hair continues to grow. Each follicle follows this cycle independently, under the control of numerous internal factors, with a central role played by hormones.

Among these hormones are the androgens, particularly testosterone and its active form, dihydrotestosterone (DHT), which are key determinants of hair density, thickness, and distribution. They trigger the conversion of fine, lightly pigmented hairs into thicker, longer, and darker ones, especially during puberty. These effects are amplified under hormonal imbalances, as observed in certain pathological conditions.

Age is also a major factor: body hair develops during adolescence, stabilizes in adulthood, and then evolves with aging. In women, the menopause can be accompanied by thinning of certain hairs and the emergence of thicker hairs in other areas due to hormonal changes. In men, areas such as the scalp may lose density while other areas become hairier. The genetics plays a crucial role as well: each individual inherits a specific hair program that determines hair distribution, density, and texture. Thus, under identical habits, two people can exhibit very different levels of body hair.

Finally, certain medical disorders directly influence hair growth. This is notably the case with polycystic ovary syndrome (PCOS), which leads to an excess of androgens in women, or with certain endocrine diseases affecting the adrenal or thyroid glands. These pathological effects on hair follicles have been detailed in recent studies describing the hormonal regulation pathways of hair growth.

In short, human body hair results from a complex interplay of hormones, genetic background, age, and health status—far more than from a purely superficial act like shaving.