The Root Causes of Hair Loss

Similar to plants, hair grows in cycles. When that rhythm is disturbed, hair loss can follow.

Illustration by The Epoch Times, Shutterstock

The roots of your hair are like a thriving miniature world.

Hair follicles surround the roots, efficiently delivering nutrients and producing essential building blocks for healthy hair growth. However, when this delicate system is disrupted, hair loss occurs.

At least 80 percent of men and nearly half of all women experience significant hair loss at some point. To effectively address hair loss, knowing how hair grows and identifying the underlying cause of loss is crucial.

The Science of Hair Growth

All vital hair activities occur within the hair follicle at its root.

The cells within the hair follicle are among the most metabolically active and rapidly dividing in the human body. The hair root has a bulb-shaped base that houses the dermal papilla, a structure rich in tiny blood vessels that supply blood and nutrients essential for hair growth.

New hair cells are continuously produced within the follicle, forming strands that gradually emerge from the skin’s surface. This process allows hair to grow at an average rate of about one centimeter per month. Notably, the number of hair follicles on the scalp is fixed—at around 100,000, with each follicle capable of producing multiple hairs over its lifetime.

Hair growth follows a cyclical pattern, much like plant growth. It begins with a prolonged growth phase that lasts between two and seven years. After this phase, the hair root disconnects from the nutrient-supplying dermal papilla and enters a resting phase. Three to four months later, the hair sheds and a new strand begins to grow, continuing the cycle.

advertisement

Hair grows in cycles, starting with a two- to seven-year growth phase, followed by a resting phase, shedding, and regrowth. Illustration by the Epoch Times, Shutterstock

Unlike plants, however, hair does not shed all at once in a single season. Instead, hair strands are in different phases at any given time, maintaining a stable distribution: 80 to 90 percent of hair is in the growth phase, and 10 to 20 percent in the resting and other phases.

A healthy adult naturally loses about 70 to 100 hairs per day.

“Scientifically, nobody goes bald because the hair is falling naturally,” Rajesh Rajput, a hair transplant surgeon and fellow of the International Society of Hair Restoration Surgery, told The Epoch Times.

However, “you go bald when fallen hair is not replaced with new hair due to interruption in the natural hair cycle,” he said.

Can Hair Loss Be Reversed?

Some types of hair loss are reversible, especially when caused by disruptions in the natural growth cycle. In these cases, the hair follicles—the foundation of hair growth—remain intact and can still produce new hair.

However, some forms of hair loss are permanent. When follicles become severely damaged and become fibrotic scars, they lose their ability to regenerate hair. This form of hair loss is classified as scarring alopecia, whereas reversible hair loss falls under non-scarring alopecia.

Premium Picks

Your Brain Flushes Out Waste Every Night–Here’s How to Help It Clean Up

Muscle: The Organ that Powers Vitality

Your Mattress May Be the Cause of Unexplained Symptoms—Here’s Why

A 2019 study conducted across multiple specialized hair clinics worldwide found that approximately 70 percent of patients seeking treatment for hair loss had non-scarring alopecia.

Regardless of the type of hair loss, there are ways to slow down or even improve the condition to some extent—though there is no one-size-fits-all solution. This series will explore various remedies and preventative approaches in detail.

Before that, however, the first step is to identify the causes of your hair loss.

Leading Causes of Hair Loss

Genetics–the Inevitable

Rodney Sinclair, a professorial fellow in the Department of Medicine at the University of Melbourne and director of Sinclair Dermatology, shared a striking case from his research.

A man working in financial consulting at McKinsey & Company had an intensely demanding job, often working 15 to 18 hours a day. When he began losing his hair, he assumed stress was the cause.

However, upon returning to Australia, he saw his identical twin brother—whose hair loss mirrored his own. Yet, over the past nine months, his brother had been living a carefree life in Byron Bay, surfing and enjoying himself.

The twins had androgenetic alopecia, a complex genetic condition known as pattern hair loss. “It is something like 80 percent genetic and less than 20 percent environmental,” Sinclair told The Epoch Times.

Hair growth is naturally induced by androgens—hormones present in both men and women. For example, before puberty, only fine hair grows in the underarm area. As androgen levels increase, coarser and darker hair begins to develop.

For some people, however, androgens inhibit hair follicle activity in certain areas of the scalp. Their hair follicles are overly sensitive to androgens, particularly dihydrotestosterone (DHT)—the most potent hormone affecting hair follicles. Compared to others, these people have more androgen receptors in the frontal hairline and crown areas, allowing DHT to bind for prolonged periods, sending continuous signals to the follicle cells. This overstimulates hair follicles and leads to progressive shrinkage and deterioration.

As a result, the hair growth phase shortens, leading to thinner, finer hair over time. Eventually, the hair becomes too weak to emerge from the scalp’s surface, leaving behind empty follicle openings.

Androgenetic alopecia is a form of non-scarring alopecia. However, if left untreated, the continuously shrinking follicles may permanently disappear, making hair regrowth impossible.

In the United States, approximately 50 million men and 30 million women are affected by this condition.

“Androgenetic alopecia is the commonest in both genders,” said Dr. David Saceda-Corralo, a dermatologist at Ramón y Cajal University Hospital in Madrid, Spain, and a researcher specializing in hair disorders. Based on his clinical experience, 70 percent of androgenetic alopecia patients are men, while 30 percent are women. He added that in females, the situation is more complex.

The pattern of hair loss in androgenetic alopecia differs between men and women.

In people with androgenetic alopecia, dihydrotestosterone (DHT) attacks their hair follicles, leading to thinner hair. The hair loss pattern is different in males and females. Illustration by The Epoch Times, Shutterstock

Male-pattern hair loss typically begins at the forehead, with the hairline gradually receding and the temples thinning. In some cases, balding also develops at the crown, and in severe cases, only the hair on the sides and back of the head remains, forming a horseshoe-shaped pattern.

In women, the hairline is usually maintained, but thinning occurs along the center part of the scalp and spreads outward in a diffuse pattern. Over time, this progressive thinning from the front to the crown creates a Christmas tree-like pattern as more of the scalp becomes visible.

“Androgenetic alopecia affects 100 percent of all men and all women as they get older,” said Sinclair.

As people age, he said, some degree of hair loss due to androgens is inevitable—the only differences are when it begins and how quickly it progresses. “There is not a 50-year-old man on the planet who’s got hair like a 15-year-old,” he noted.

Stress

While the carefree twin in the previous case also experienced hair loss, this does not negate the role of stress, which—independent of genetic factors—is a well-established trigger for hair shedding.

Hair follicles are highly responsive to stress—in addition to containing receptors for stress hormones, they can also produce these hormones themselves.

A notable discovery is that the cortisol concentration in hair strands—particularly in the 3 centimeters closest to the scalp—can serve as a biological record of cumulative stress levels over the past three months.

When stress hormones bind to follicle receptors, they disrupt normal hair growth and accelerate shedding. Additionally, stress interferes with the follicle’s ability to re-enter the growth cycle, preventing hair regrowth. A 2021 animal study published in Nature indicated that stress hormones prolong the resting phase of hair follicle stem cells, significantly delaying hair regeneration.

Psychological stress also triggers the release of neuropeptides, which stimulate the nervous and immune systems. An overactive immune response can mistakenly attack hair follicles, leading to alopecia areata, an autoimmune disorder that causes patchy hair loss. Additionally, these neuropeptides have been shown to induce and accelerate programmed cell death in follicle cells, further exacerbating alopecia areata.

Sleep Disorders

In addition to work and daily life pressures, poor sleep quality and frequent late nights—increasingly common in modern society—can contribute to hair thinning and loss.

A systematic review found a significant bidirectional causal relationship between sleep disorders and alopecia areata. In a study involving 25,800 patients with sleep disorders and 129,000 individuals with normal sleep patterns, researchers observed that those with sleep disorders had a 65 percent higher risk of developing alopecia areata, with the effect being particularly pronounced in young and middle-aged people. A Taiwan study reported an even greater risk increase—4.7 times higher.

advertisement

Another study identified obstructive sleep apnea (OSA)—a condition characterized by snoring and disrupted breathing during sleep—as a potential risk factor for male-pattern hair loss in men with a family history of hair loss. Specifically, those with both OSA and a genetic predisposition to hair loss were seven times more likely to develop androgenetic alopecia compared to those without these factors.

Additionally, a 2023 study found that androgenetic alopecia was significantly associated with poor sleep quality and a total sleep time of less than six hours per night.

Physiological Stress

More than 90 percent of women experience diffuse, excessive hair shedding around three to four months after giving birth. Many new mothers find excessive hair on their pillows and shed clumps while washing, leading to visibly thinner hair—an unsettling experience that often triggers significant anxiety.

This phenomenon is linked to hormonal fluctuations during and after pregnancy. Specifically, elevated hormone levels during pregnancy prolong the growth phase, keeping more hair in place than usual. However, these hormone levels drop sharply after childbirth, triggering a mass shift of follicles from the growth phase to the next phase. As a result, the resting phase occurs collectively a few months later, leading to noticeable postpartum hair loss.

Postpartum hair loss is a common form of telogen effluvium, a temporary condition in which excessive hair shedding occurs due to disruptions in the hair growth cycle. Typically, the shed hair regrows within a few months, and hair density gradually returns to normal.

Childbirth is not the only trigger. Hormonal imbalances, illness, surgery, certain medications, and even COVID-19 infections can place the body under significant stress, leading to telogen effluvium. In most cases, hair growth resumes once the underlying stressor is resolved.

“Hair has [the] lowest priority in the body,” Rajput said. When the body faces illness or imbalance, it redirects energy away from hair growth to sustain essential survival functions. This is why people often experience hair loss after a physical crisis.

Everyday Causes of Hair Loss

Many everyday causes of hair loss are avoidable.

The Effects of Some Foods

As mentioned earlier, hair follicles have high metabolic activity and require a steady supply of nutrients to support hair growth. These nutrients are delivered through the bloodstream via a dense blood vessel network, serving as the building blocks for hair production.

“A huge number of nutrients are required for hair growth,” Rajput said.

Ultra-processed foods lack essential nutrients and contain excess sugar and unhealthy fats that disrupt hormonal balance and impair hair growth. Additives such as nitrates and phosphates can trigger inflammation and oxidative stress, further damaging hair follicles.

An animal study found that switching to a high-fat diet caused diffuse hair loss in healthy mice, while those fed a high-fat diet from an early age exhibited a decreased number of hairs and struggled with hair regeneration.

Rajput stated that junk food increases toxin buildup, free radicals, and reactive oxygen species in the body. “the cells have become so weak with the accumulation of toxins that even normal hormone levels can negatively affect them,” he added.

Excessive consumption of high-glycemic foods rich in simple sugars, such as refined grains and sugary beverages, can also contribute to hair loss. Furthermore, high insulin levels impair scalp blood circulation, reducing oxygen supply to hair follicles.

“A diet high in sugars and processed foods can indirectly lead to hair loss,” Cindy Chan Phillips, a registered dietitian, said in an interview with The Epoch Times.

Hair Washing Frequency

The scalp and hair accumulate impurities, including sebum, dead skin cells, product residue (such as hair gel), dust, pollen, and even tobacco smoke. The scalp also harbors microbes, and without proper cleansing, dirt and excess bacteria accumulate, affecting the scalp and follicle health.

Unwashed sebum oxidizes and clogs hair follicles, leading to itchiness, scalp sensitivity, and increased hair shedding. Studies have observed that itch severity significantly increases within 72 hours after the last shampoo, accompanied by increased sebum buildup.

However, excess shampooing can lead to potential damage to the hair and may outweigh the benefits. Certain shampoos contain harsh surfactants—such as sulfates—that can weaken the hair, making it frizzy and fragile while also drying out the scalp.

Ponytails and Hats

Hairstyles such as high buns, tight ponytails, tightly woven braids, and hair extensions place tension on the scalp, pulling on hair follicles. Over time, this can cause inflammation and follicle damage and ultimately lead to traction alopecia—a type of hair loss caused by prolonged stress on the follicles. It is most severe in areas under the greatest strain, typically along the hairline.

In addition to hairstyles, wearing tight hats or headpieces for extended periods can cause traction alopecia. Hats that are too tight, warm, or rarely washed can restrict blood flow to hair follicles and trap sweat and sebum, further compromising scalp health.

Key Facts

“There are more than [a] hundred types of hair loss. Some alopecias share the same characteristics or symptoms,” said Saceda-Corralo.

For the average person, determining the cause of hair loss through observation alone is difficult. A proper diagnosis requires evaluation by a specialist. During consultations, doctors typically perform biochemical tests alongside specialized assessments such as trichoscopy—a high-resolution imaging technique used to examine the scalp—before identifying the specific type of hair loss.

Saceda-Corralo also noted that people can experience multiple types of hair loss simultaneously. For example, a woman may have both androgenetic alopecia and telogen effluvium at the same time.

“It is much easier to prevent hair loss than to try and regrow it once lost,” said Sinclair, urging those experiencing hair loss to seek early diagnosis and treatment.

Hair growth follows a natural cycle, and some treatments need to be used consistently for several months before noticeable results appear. Long-term commitment is necessary to maintain the benefits.

Next: Before we talk about diet, lifestyle habits, and natural remedies, let’s first take a closer look at the common hair loss medications and treatments: Are they effective, and what are the risks?