Common misconception: hair becomes thicker and regrows more quickly when you shave it

Contrary to a widespread misconception, shaving neither alters hair density, thickness nor the rate of hair regrowth. This illusion stems from a purely visual and tactile phenomenon. When shaving a hair, it is cut at the surface of the skin, at the level of the hair shaft. The hair is then cleanly severed, giving it a straight, rigid end, in contrast to a natural hair whose tip is tapered. This can make it feel pricklier to the touch, more noticeable and give it a thicker appearance. It may also appear darker because freshly cut hair has not yet been exposed to light or external agents that gradually lighten it over time. Finally, the simultaneous regrowth of several hairs cut at the same time can create the impression of increased density.

The study conducted by Aliakbarpour et al. (2017), published in the Journal of Cosmetic Dermatology, aimed to determine whether shaving hair could influence their growth, thickness or density compared with a scissors cut. This question is particularly relevant in the context of preparing for laser hair removal in women with hirsutism, a disorder characterised by excessive hair growth in areas that are normally sparsely hairy in women, due to an excess of androgens.

To address this question, researchers conducted a randomised clinical trial involving 60 women with hirsutism (defined as the appearance of hair in so-called male areas, which are normally hair-free in women). The participants were divided into two groups: one group was instructed to shave the treatment areas, while the other was asked to trim the hair with scissors before beginning the laser sessions. The study lasted 12 weeks, with regular follow-up of the patients and an objective assessment of hair regrowth. The researchers evaluated several parameters: hair density, hair thickness, regrowth rate and the efficacy of the laser treatment according to the preparation method used. The results showed that no significant difference was observed between the two groups regarding regrowth rate or hair thickness. In other words, shaving did not make the hair thicker or more numerous. Furthermore, the efficacy of the laser treatment was not affected by the chosen hair removal method. This study therefore confirms that shaving, contrary to a persistent misconception, does not alter hair quality or its growth cycle, even in a specific hormonal context such as hirsutism. It reinforces existing literature data on the illusory nature of post-shaving hair thickening.

Human body hair is regulated by complex biological mechanisms that act mainly at the level of the hair follicle, a structure located in the dermis. This follicle follows a hair cycle comprising 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. This is followed by the catagen phase, a short transition phase of about three weeks, during which the follicle undergoes involution: the hair loses its connections with the papilla and retracts. The telogen phase, or resting phase, follows for about three months; it is a period of almost zero cell proliferation, the papilla retracting to an area near the bulge, without notable 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, the androgens, notably testosterone and its active form, the dihydrotestosterone (DHT), are key determinants of hair density, thickness and distribution. They induce the transformation of fine, lightly pigmented hairs into thicker, longer and darker hairs, particularly during puberty. These effects are amplified in cases of hormonal imbalance, as can be observed in certain pathologies.

Age is also a major factor: hair growth increases during adolescence, stabilises in adulthood, then changes with ageing. In women, the menopause may be accompanied by thinning of certain hairs and the appearance of coarser hairs in other areas, as a result of hormonal changes. In men, areas such as the scalp can lose density while other regions become hairier. The genetics also plays a crucial role: each individual inherits a specific hair-growth programme that determines the distribution, density and texture of their hair. Thus, with identical routines, two people can display very different levels of hairiness.

Finally, certain medical conditions directly affect hair growth. This is particularly evident in polycystic ovary syndrome (PCOS), which leads to androgen excess in women, or in certain endocrine disorders affecting the adrenal or thyroid glands. These pathological effects on hair follicles have been detailed in recent studies that describe the hormonal regulatory pathways of hair growth.

To summarise, human body hair results from a complex interplay of hormones, genetic makeup, age and health status, rather than simply from a superficial act such as shaving.

• Macwilliams P. & al. Shaving and hair growth. The Journal of Investigative Dermatology (1970).

• HATTORI M. & al. Regulation mechanisms of hair growth. Current Problems in Dermatology (1983).

• Androgens and hair growth. Dermatologic Therapy (2008).

• ALIAKBARPOUR F. & al. A randomized clinical trial on the comparison between hair shaving and snipping prior to laser hair removal sessions in women suffering from hirsutism. Journal of Cosmetic Dermatology (2017)

• MECZEKALSKI B. & al. Hormonal Effects on Hair Follicles. International Journal of Molecular Sciences (2020).

• ALADRAJ J. F. & al. Effects of Hormones and Endocrine Disorders on Hair Growth. Cureus (2022).