While many men lose hair on top of their heads over time and at different ages, their eyebrow, ear and nose hair never stops growing, as if it had been dipped in a magical elixir of life. In contrast, women's hair, including eyebrows, tends to grow. to shedding with their age.

What is the scientific explanation for the increase in the density of different facial hairs in men in old age, while the opposite does not happen in women?

The effect of hormones on men and women

According to Dr. Danilo del Campo, a dermatologist at the Chicago Skin Clinic, he tells Live Science, older men's hair is affected by elevated levels of hormones, specifically testosterone, until aging.

These hormones have greater effects on the hair follicles over time.

While estrogen, which increases hair growth and diameter, tends to decrease in postmenopausal women, according to a 2020 review in the International Journal of Molecular Sciences.

Dr. Mary Jane, M.D., chief of dermatology in San Carlos, California, tells Live Science that hair growth and how quickly it grows, its texture and color depends mainly on genetics, age, nutrition, health and gender.

But as people age, hormones and different responses to hormones are the main reason for the difference between males and females when it comes to hair.

Hair growth, how fast it grows, its texture and color depends mainly on genetics, age, nutrition, health and gender (Getty Images)

How does eyebrow hair grow?

All body hair grows from hair follicles whose life cycle consists of 3 phases, the growth phase, the two-week transition phase and the months-long dormant phase.

After the hair follicles become dormant, the hair eventually falls out, and then the anagen phase begins again.

The length of body hair is different from one part to another, because the lengths of these stages vary.

Scalp hair has the longest anagen phase, which usually ranges from two to seven years, says del Campo.

However, eyebrow hair and other hair-bearing sites are completely different.

The shorter the anagen phase of the hair follicle, the shorter the hairs in this part of the body.

“Eyebrows have a very short growth phase of about 30 days,” Del Campo says. “This short growth period is followed by an extended resting phase, which explains why brow hairs are usually 1cm or less.

"If the growth phase is longer, people will have to use scissors at the barber to trim their eyebrows very frequently," he adds, a grooming requirement that becomes essential for some men as they age.

The role of testosterone

The lengths of the different phases are affected by the hormones circulating in the body.

"The hair cycle, as well as the structure of the hair follicle, is strongly influenced by various hormones," Jane says.

In particular, men often have high levels of androgens, the group of hormones responsible for the development of male characteristics in the body, especially testosterone, while women tend to have low levels of androgens. These androgens are the reason men's hair grows faster.

During puberty, these androgens are responsible for hair growth in places such as the face, arms, and back.

Jane says that these androgens act as hair stimulators in certain parts of the body such as the pubic area, chest, face and armpits during puberty.

As men age, some hair follicles become more sensitive to these hormones.

Because the follicles become more sensitive to androgen, hormones keep them developing longer, which leads to more hair growth with age in places like the eyebrows, nose and ears.

Hair follicles on the scalp react differently to testosterone resulting in baldness (pixels)

Thick eyebrows and a bald head

Interestingly, and somewhat mysteriously, hair follicles on the scalp react differently to testosterone, which actually shortens their growth cycle when testosterone levels increase, which is why some older men have thicker eyebrows. He had long nose hair and full ear hair, but his head was bald.

As women age, estrogen levels decline during menopause.

It is believed that these hormonal changes and other factors in aging lead to thinner and less dense hair in women.

"While men continue to produce androgens until the age of 70, women's hormones become depleted with menopause at the age of 50," Jane says.

Loss of eyelashes and eyebrows

Some conditions can cause people to lose eyebrows or eyelashes.

Alopecia, also known as patchy hair loss, can affect both.

Sometimes, the eyelashes fall out for unknown reasons, or a person may pull out their eyelashes either because they are bothersome or because of anxiety.

In other cases, people with a condition known as trichotillomania have to pull their hair.

An underactive thyroid can cause eyebrows to thin, and lupus can cause them to fall out.

If you notice that your eyebrows or eyelashes are falling out or changing in another way, see a doctor.