What Causes Hair Loss? Genetics, Hormones, Habits and Health Conditions Explained

What Causes Hair Loss? Genetics, Hormones, Habits and Health Conditions Explained

• August 27, 2026
• Dr. Arthur Zacco

Last updated on August 27, 2026

Quick answer: Most hair loss comes down to a short list of causes. Genetics is the largest single factor, followed by hormonal change, stress, nutritional deficiency, medical conditions such as diabetes and thyroid disease, certain medications, and hairstyles that pull constantly on the follicle. Some are permanent and some are fully reversible, and the difference matters, because treatment depends entirely on which one you have.

How Hair Growth Works

Every strand cycles through three phases, and understanding them explains why shedding is normal and when it is not. It is normal to lose 50 to 100 hairs a day, which is a small number against the roughly 100,000 hairs a healthy scalp produces.

Anagen: the growth phase

The active growth stage, containing 85 to 90 percent of your hair at any given time. Follicles are rooted deep in the scalp producing new cells that push upward to form the hair shaft. Anagen lasts two to seven years depending on genetics, age and health, which is why some people grow hair very long and others find it never passes a certain length.

Catagen: the transition phase

A short stage of roughly 10 to 14 days affecting about 5 percent of hairs. Growth stops, the follicle shrinks and disconnects from its blood supply, and the hair forms a club hair that anchors it before shedding. If unusually large numbers of hairs enter catagen at once, that often signals stress, illness or hormonal imbalance.

Telogen: the resting and shedding phase

Telogen lasts two to four months and covers 10 to 15 percent of hairs. The hair rests before shedding to make room for a new anagen hair from the same follicle. When too many hairs shift into telogen at once, the result is telogen effluvium, the diffuse shedding that appears two to three months after a trigger.

The Main Causes of Hair Loss

Genetics

Androgenetic alopecia is the most common form of hair loss in both men and women, and the Journal of Dermatology and Skin Science estimates it affects around 80 million people in the United States. In men it shows as a receding hairline or thinning at the crown, driven by DHT, a byproduct of testosterone. In women it appears as diffuse thinning with a widening part line. It is progressive, but early intervention slows it substantially.

Hormonal Changes

Hormones regulate the hair cycle directly. In women, pregnancy, childbirth, menopause and stopping birth control all trigger shedding, as do PCOS and thyroid imbalance. In men, both high and low testosterone can contribute. Hair often recovers once the imbalance is corrected, which is why blood work for thyroid and hormone levels is a standard first step.

Stress and Trauma

Major surgery, illness, bereavement or sustained psychological stress can push large numbers of hairs into the resting phase. The shedding is delayed, which is why many people fail to connect it to an event two or three months earlier. This type of loss is usually temporary and resolves as the trigger passes.

Nutritional Deficiency

Hair follicles are among the most metabolically active cells in the body and suffer quickly when nutrients run short. Deficiencies in iron, zinc, vitamin D, biotin, iodine and protein all contribute to shedding and brittle strands. Iron deficiency in particular is well documented as a cause of shedding in both men and women. Crash diets and digestive conditions that impair absorption are frequent culprits.

Diabetes and Blood Sugar

Diabetes affects hair growth through several routes at once. It damages blood vessels and reduces circulation to the scalp, limiting the oxygen and nutrients follicles need. Insulin resistance disrupts the hormonal rhythm of the growth cycle, and diabetes raises the risk of autoimmune conditions such as alopecia areata. Some diabetes medications also list hair thinning as a side effect.

Diabetes-related loss usually presents as diffuse thinning rather than distinct bald patches, sometimes with slower regrowth and finer hair. In most cases hair regrows once blood sugar is controlled, though recovery takes time and may be incomplete if follicles have been damaged by prolonged poor circulation.

Other Medical Conditions and Medications

Thyroid disorders, autoimmune conditions including alopecia areata, scalp infections and chronic illness can all disrupt the cycle. Medications for blood pressure, depression, cancer and high cholesterol commonly list hair loss as a side effect. Never stop a prescribed medication without supervision, but do raise it with your doctor, as switching drugs is often possible.

Styling Tension and Damage

Tight braids, locks, weaves, ponytails and buns worn continuously cause traction alopecia, where repeated pull damages the follicle. It typically starts at the hairline and temples, is reversible early on, and becomes permanent if tension continues. Aggressive bleaching, relaxers and heat styling weaken the shaft and cause breakage rather than true follicle loss.

Age

Hair naturally becomes finer and less dense with age. For women this accelerates around menopause as estrogen declines, and for men genetic loss continues progressing. Age-related thinning is normal, but it is not untreatable.

Everyday Habits That Damage Hair

Several routine habits contribute to breakage and thinning:

• Overusing heat tools. Limit flat irons and dryers, use the lowest setting suitable for your hair type, and always apply a heat protectant.
• Brushing wet hair. Wet hair is at its most fragile. Use a wide-tooth comb or a brush designed for wet hair.
• Harsh chemical treatments. Ammonia and peroxide in dyes, and sodium hydroxide in relaxers, weaken both hair and scalp. Have these applied professionally.
• Chlorine exposure. Wear a swim cap and rinse thoroughly after swimming.
• Crash dieting. Rapid restriction deprives follicles of protein and micronutrients, triggering shedding months later.
• Chronic stress. Sustained stress disrupts the growth cycle. Exercise, sleep and relaxation all help.

Hair Loss Myths, Debunked

Myth: cutting your hair prevents hair loss

Haircuts remove split ends and make hair look fuller, but they have no effect on growth rate or on how much hair you lose. Growth happens at the follicle, below the skin, where scissors cannot reach.

Myth: hair loss only affects older people

With a family history, genetic hair loss can begin in the teens or twenties, and nutritional deficiency and stress cause shedding at any age. Roughly half of men show noticeable pattern loss by 50, but it usually starts decades earlier.

Myth: shampoo and styling products cause hair loss

Regular washing keeps the scalp clean and supports healthy growth, and losing a few hairs in the shower is normal. Sulfates are not linked to hair loss, though they can irritate sensitive skin and strip color from dyed hair, so sulfate-free shampoo is a choice for comfort rather than a hair loss treatment. Most styling products are equally harmless provided you wash often enough to prevent buildup.

Myth: wearing a hat causes baldness

Hair growth depends on blood flow to the follicle, and a normally fitted hat does not restrict it. The myth persists because people wear hats to cover thinning already underway. A dirty or greasy hat can contribute to folliculitis, so wash them.

Myth: hair loss is always permanent

Loss from stress, illness, deficiency, hormonal change or tension hairstyles is frequently reversible once the cause is addressed, and genetic loss responds to early treatment. Only scarring alopecia, where the follicle is destroyed and replaced with scar tissue, is truly irreversible.

When to See a Doctor

Book an assessment if you notice any of the following:

• Shedding that continues beyond two to three months
• A widening part line, receding hairline or visible scalp
• Patchy or circular areas of loss
• Hair loss alongside fatigue, weight change, excessive thirst or slow wound healing
• A sore, scaling, inflamed or persistently itchy scalp

Time matters. Miniaturized follicles can often be stimulated back into productive growth, but once a follicle has fully atrophied, non-surgical treatment is far less effective.

Treatment Options in Raleigh, NC

Effective treatment starts with an accurate diagnosis, because the same symptom can have very different causes. At AZ Hair Restoration, Dr. Zacco evaluates scalp health, medical history and hormonal or nutritional status first. Where follicles are still active, non-surgical hair loss treatments including Growth Factor Therapy and exosome therapy can stimulate them back into the growth phase. Where follicles are no longer producing hair, hair transplant procedures such as FUE and FUT restore density permanently. Different types of alopecia call for different approaches, which is why the assessment comes first.

Dr. Zacco has been performing hair transplantation in Wake County, North Carolina, since 1996. To find out what is behind your hair loss, schedule a free consultation at our Raleigh clinic or call 919-830-3778.

Frequently Asked Questions

What causes hair loss?

Genetics, in the form of androgenetic alopecia, is the most frequent cause. Hormonal shifts from pregnancy, menopause, thyroid disorders or PCOS are also common, as are stress, deficiencies in iron, zinc, vitamin D or protein, medical conditions such as diabetes and autoimmune disease, certain medications, and hairstyles that place constant tension on the follicles.

How much hair loss is normal?

Losing 50 to 100 hairs a day is normal. At any moment roughly 85 to 90 percent of scalp hair is actively growing, so ongoing shedding is expected. Concern is warranted when shedding noticeably increases, when the scalp becomes visible through the hair, or when the hairline or part line starts to widen.

What is the difference between hair shedding and hair loss?

Shedding is temporary. Hairs fall out faster than usual after a trigger such as illness, childbirth or stress, but the follicles remain healthy and regrowth follows. Hair loss means regrowth has slowed or stopped, usually because of genetics, hormones or follicle damage. Shedding shows as sudden diffuse loss, while genetic hair loss shows as gradual thinning in a pattern.

Does diabetes cause hair loss?

Diabetes can contribute to hair loss. It damages blood vessels and reduces circulation to the scalp, limiting the oxygen and nutrients follicles need. It also disrupts hormones and raises the risk of autoimmune conditions such as alopecia areata. Diabetes-related loss usually appears as diffuse thinning rather than bald patches, and often improves once blood sugar is controlled.

Does wearing hats or washing your hair cause hair loss?

No. Hair growth depends on circulation to the follicle, and a normally fitted hat does not restrict it. Washing removes oil and buildup that would otherwise irritate the scalp, and losing a few hairs while washing is normal. Sulfates in shampoo have not been shown to cause hair loss, though they can irritate sensitive skin.

Is hair loss permanent?

Not always. Hair loss from stress, illness, nutritional deficiency, hormonal change or tension hairstyles is often reversible once the cause is addressed. Genetic hair loss is progressive and needs ongoing management rather than a one-time fix. Scarring alopecia destroys the follicle and is permanent. Only a medical evaluation can determine which type you have.

When should I see a doctor about hair loss?

See a doctor if shedding continues beyond two to three months, if you notice patchy loss or a widening part line, if hair loss comes with symptoms such as fatigue, weight change or excessive thirst, or if the scalp is sore, scaling or inflamed. Early assessment protects the follicles you still have.

Medical Disclaimer

The content of this article is provided for general information and educational purposes only. It is not medical advice, and it is not a substitute for diagnosis or treatment by a qualified healthcare professional. Reading this page does not create a doctor and patient relationship. Individual results vary, and different causes of hair loss can look very similar while requiring entirely different treatment. Always consult a physician or board certified dermatologist regarding any medical concern, and never delay or disregard professional medical advice because of something you have read here. If you are experiencing sudden extensive hair loss, a painful or infected scalp, or hair loss alongside other unexplained symptoms, seek medical care promptly.

Reviewed for medical accuracy by Dr. Zacco, AZ Hair Restoration, Raleigh, NC.