Hair loss can be a distressing experience, whether it occurs gradually over time or more suddenly. It affects millions of people across all genders and ages, and while it’s incredibly common, the causes can be complex and often misunderstood. Understanding why hair loss happens is the first step in identifying the right treatment and managing expectations.

Let’s break down the most common causes of hair loss, the science behind it, and what signs you should be aware of if you think you’re losing more hair than usual.

The Hair Growth Cycle

To understand hair loss, we need to start with the basics—the natural hair growth cycle. Hair grows in three distinct phases:

1. Anagen (Growth Phase): This is the active growing phase, which can last from 2 to 7 years. At any given time, about 85–90% of the hairs on your scalp are in this phase.

2. Catagen (Transition Phase): A short, two- to three-week phase where the hair follicle shrinks and detaches from the blood supply.

3. Telogen (Resting Phase): Lasting around 2 to 4 months, during this phase, the hair stops growing and eventually falls out to make way for new hair.

Everyone naturally loses 50 to 100 hairs per day as part of this cycle. But when more hairs than usual enter the resting phase—or when new hairs don’t grow in to replace the ones that fall out—visible hair loss becomes noticeable.

1. Genetics: The Most Common Cause

By far the most common reason for hair loss is androgenetic alopecia, often referred to as male-pattern or female-pattern baldness. This type of hair loss is genetic and is driven by hormonal changes, particularly by the effects of dihydrotestosterone (DHT), a derivative of testosterone.

In genetically susceptible individuals, DHT binds to receptors in hair follicles, causing them to shrink over time. This process, called miniaturization, results in thinner, shorter hairs. Eventually, the follicles become so small that they stop producing hair altogether.

In men, androgenetic alopecia typically starts with a receding hairline and thinning at the crown. In women, it tends to appear as diffuse thinning over the top of the scalp, while the hairline remains intact.

2. Stress and Shock: Telogen Effluvium

When the body undergoes significant stress—whether physical, emotional, or physiological—it can disrupt the hair growth cycle. This condition is known as telogen effluvium.

Triggers of telogen effluvium can include:

• Severe illness or surgery

• High fever

• Childbirth (commonly called postpartum hair loss)

• Rapid weight loss

• Emotional stress

• Certain medications

These stressors push more hairs than usual into the telogen (resting) phase prematurely. A few months later, those hairs fall out all at once, leading to diffuse thinning across the scalp. Fortunately, this condition is usually temporary, and hair typically regrows once the trigger is resolved.

3. Nutritional Deficiencies

Hair is not an essential organ, so when your body lacks key nutrients, it prioritizes other systems and slows down hair production. Some of the most common nutritional deficiencies that can cause hair loss include:

• Iron deficiency: Especially common in women, low iron levels can lead to anemia and impact hair follicle function.

• Vitamin D deficiency: Vitamin D plays a role in follicle cycling, and a lack of it has been linked to hair thinning.

• Protein deficiency: Hair is made of keratin, a protein, so a lack of dietary protein can slow hair growth.

• Zinc, biotin, and B vitamins: These are crucial for healthy hair metabolism.

If you suspect a nutritional cause, blood tests can help identify deficiencies, and dietary changes or supplements may help.

4. Hormonal Imbalances

Hormones play a critical role in regulating hair growth. When they’re out of balance, hair follicles may respond by producing weaker, finer hairs—or stopping hair production entirely.

Hormonal causes of hair loss include:

• Thyroid disorders: Both hypothyroidism and hyperthyroidism can lead to hair thinning.

• Polycystic ovary syndrome (PCOS): Affects hormone levels in women and often leads to hair thinning, especially at the crown.

• Menopause: The drop in estrogen and progesterone levels can contribute to hair loss.

• Birth control pills or hormone replacement therapy: Can cause temporary shedding when starting or stopping.

Hormonal hair loss may be accompanied by other symptoms like irregular periods, acne, or weight changes. Blood tests and proper diagnosis are essential for treatment.

5. Medical Conditions and Medications

Hair loss can also be a side effect of various medical conditions or medications. For example:

• Autoimmune conditions like alopecia areata cause the immune system to mistakenly attack hair follicles, leading to round patches of hair loss.

• Lupus, diabetes, and other systemic illnesses can also impact hair growth.

• Cancer treatments, especially chemotherapy, target rapidly dividing cells—including hair matrix cells—leading to sudden and dramatic hair loss.

• Medications like beta-blockers, antidepressants, and blood thinners can also trigger telogen effluvium.

In these cases, managing the underlying condition or adjusting medications under medical supervision is key.

6. Hairstyling Practices and Physical Damage

Sometimes hair loss isn’t coming from within the body but from external factors. Traction alopecia is caused by hairstyles that pull tightly on the hair over time, such as braids, ponytails, or extensions. Chemical damage from bleach, relaxers, or heat styling can also weaken hair shafts and cause breakage that mimics hair loss.

Over time, repetitive damage can lead to permanent scarring and loss of hair follicles. The best prevention is to minimize physical and chemical trauma to the scalp and hair.

7. Scarring Alopecia (Cicatricial Alopecia)

Scarring alopecia refers to a group of rare disorders where inflammation destroys hair follicles and replaces them with scar tissue. Conditions such as lichen planopilaris, discoid lupus, and central centrifugal cicatricial alopecia (CCCA) fall into this category.

Unlike other types of hair loss, scarring alopecia can cause permanent loss if not diagnosed and treated early. Symptoms may include itching, burning, or scalp tenderness along with visible thinning or bald patches.

A scalp biopsy is often necessary to confirm the diagnosis, and treatment typically involves anti-inflammatory medications to stop the progression.

When to See a Hair Specialist

If you notice sudden shedding, visible thinning, or patches of hair loss, it's worth consulting a hair restoration specialist or dermatologist. Early diagnosis can make a big difference in identifying reversible causes or slowing progressive ones.

Hair loss is rarely just a cosmetic issue—it often reflects what’s happening beneath the surface. That’s why taking a comprehensive approach that includes medical history, lab work, and sometimes even scalp imaging or biopsy can help uncover the root cause.

Final Thoughts

Hair loss happens for many different reasons—some are genetic and inevitable, while others are triggered by lifestyle, stress, or health conditions. The good news is that there are more effective treatment options than ever before, from medications like finasteride and minoxidil to cutting-edge therapies like PRP, exosome injections, and hair transplantation.

Understanding why you're losing hair is the first step toward finding the right solution—and in many cases, regaining not just your hair, but your confidence as well.