Top things to know:
Some people report more bad hair days around their period
The production of oil which exits from the same route as your hair follicle is influenced by your hormones
Your hair may change during different life stages, like pregnancy and menopause
How hair changes throughout the menstrual cycle
Your skin and scalp change in response to hormonal variations occurring throughout your cycle. Some people report more bad hair days around their period (1).
Many of the changes you may be associating with your hair throughout your cycle are due to the changes in oil production from your sebaceous glands. Since sebum (oil produced by the sebaceous gland) and the hair follicle exit from the same opening in the skin, the hair and skin surrounding may be coated in sebum.
Sebum production is influenced by your hormones, particularly androgens (like testosterone) (2,3).
Sebum production often ramps up greatly during puberty, often being produced at high amounts between the ages of 15 to 35, as assessed on the skin (4). Estrogen also influences sebum production, particularly by suppressing levels of sebum production and sebaceous gland activation, especially at high doses (2,3,5-7). In a study of sebum production on the skin, people with oily-type skin noticed an increase in sebum production during their premenstrual and menstrual period, with the lowest amount of sebum production during the second week of their cycle (8).
One study ('Bad hair days', scalp sebum excretion and the menstrual cycle) had an interesting finding: even if more bad hair days were registered around the time of menstruation, they did not correlate with increases in scalp sebum levels (1). There was not a clear explanation for the bad hair days—perhaps it’s due to a difference in participants’ personal perception of their hair (1). Is the change on your head or in your head?
Some hormonal contraceptive medications (like chlormadinone acetate, a synthetic progesterone which provides anti-androgen activity) may also affect hair and skin quality (9). In one study of people taking these medications (Effects of an oral contraceptive containing chlormadinone acetate and ethinylestradiol on hair and skin quality in women wishing to use hormonal contraception), participants had decreased sebum production and improved perceived hair quality (9).
Understanding hair anatomy
If you’re curious about changes to your hair and suspect they might be linked to hormonal changes, it’s helpful to understand the anatomy of hair.
There are many different types of hair that grow on your body, differing in texture, length, type, and density. Think of the difference between the hair on your head versus the fine hair on your torso. The only areas of our skin without hair growth are on the palms of hands, the soles of feet, and lips (10).
Each individual hair grows out of hair follicles. The part of the hair that you can see exiting your skin is called the hair shaft.
Each hair follicle is part of a pilosebaceous unit within the skin, which consists of a hair follicle, a sebaceous gland, and a small muscle called the arrector pili. The sebaceous gland produces an oil called sebum, which exits onto the skin through the same route of the hair.
The arrector pili is a very small muscle that is attached to each individual hair follicle. When you are cold or scared, you may notice that your skin turns bumpy and the hairs on your body stand on end (goose bumps)—you can thank this tiny muscle for this. Some hairs, like the hairs on your head, can be in their active growing phase for many years, while other hairs, like the ones on your eyebrows, may only grow for a couple of months before they are shed (11).
There are three phases of a hair’s life cycle. The growing phase (anagen phase), the end of the active growth of the hair (catagen phase), and the final resting phase where the hair is dead and will eventually fall out (telogen phase) (10,11). Losing hairs every day is part of the natural life cycle of the hair—losing between 50 to 150 scalp hairs per day is normal (11).
Hair changes in pregnancy, menopause, and PCOS
During pregnancy, some people may notice increased hair thickness. This is because the number of hairs shed daily is reduced. Pregnancy influences hair follicles to stay within their growth phase (anagen phase) longer than they would normally (12).
After delivery, it is normal to notice increased amounts of hair loss, as all the hairs that stayed in prolonged anagen phase change over together into catagen phase (11,12). This is considered common and should not be any reason to panic. Even if it feels like you may be losing an abnormal amount of hair, it is just an accumulation of all the hair you would have normally lost during the time you were pregnant (12).
Other changes that can occur to your hair during pregnancy are an increase in hair fiber diameter—i.e. hair thickness—as it grows from the scalp, in comparison to women who were not pregnant (13). This change in hair diameter may also contribute to feelings of increased hair thickness during pregnancy.
Hair growth may also change around the time of menopause, as sex hormone levels change in availability. Some people may notice they develop female pattern hair loss, where their hairline may stay the same, but hair follicle density decreases around the top and sides of the head (12). Facial hirsutism (abnormal hair growth) is also common after menopause, with around half of post-menopausal women reporting excessive facial hair growth (12,14).
Another very common cause of hirsutism is polycystic ovarian syndrome (PCOS), in which androgen levels are abnormally high. In both PCOS and after menopause, the levels of androgens are relatively higher. This excess in androgens promotes hair to grow thicker, darker, and increase sebum production (10,12).
What’s average and healthy
Every person’s hair is different, just as every body is different. Color, length, thickness, curl—there is no such thing as average or normal hair—only what is “average and normal” for you. Hair is very different from person to person.
Some researchers have tried to assess the speed at which hair grows, and they found that scalp hair grows about 15 cm (6 inches) a year, or 1.25 cm (0.5 inches) per month (15).
There are many other culprits other than your hormones that can account for a bad hair day. These include environmental factors (smog, smoke, exposure to UV light, saltwater), hair care products, perming, bleaching, hair dyeing, excessive use of hair products, infrequent washing, rough brushing, and excessive heat styling (1,16).
Use Clue to track how your hair changes throughout your cycle.
You can track your hair daily as “Good”, “Bad”, “Oily”, or “Dry”. If you want to track more, you can .