What Causes Hair Loss, and Which Treatments Are Actually Proven?

Quick answer: The most common cause of hair loss is androgenetic alopecia (genetic pattern hair loss). It affects about half of men by age 50 and becomes more common in women after menopause. Other major causes include telogen effluvium (shedding triggered by stress or illness), alopecia areata (an autoimmune condition), thyroid problems, nutritional deficiencies, medications, and traction from tight hairstyles. Two treatments are FDA-approved for hair loss: topical minoxidil and oral finasteride. Several others, including oral minoxidil, dutasteride, PRP, low-level laser therapy, and microneedling, have meaningful clinical evidence and are widely used off-label.

Hair loss is one of the most searched health topics in the U.S., and one of the most misunderstood. Many people start in the supplement aisle because the marketing is simple, but most of those products have little clinical backing. The treatments with the strongest evidence have been around for decades and are often overlooked.

This guide explains the seven most common causes of hair loss in plain language, then walks through each major treatment and what the evidence says about it. It's written for anyone who has noticed more hair in the shower drain or is weighing options after a dermatologist visit.

About this article: This article is for general information. It draws on peer-reviewed clinical research, FDA guidance, and guidelines from the American Academy of Dermatology (AAD). It is not a substitute for personal medical advice. If you're losing a lot of hair, see a board-certified dermatologist.

What Are the Most Common Causes of Hair Loss?

Hair loss is a symptom, not a single condition, and the right treatment depends on what's causing it. A multicenter study of 22 specialist hair clinics, summarized in NIH StatPearls, looked at 2,835 patients, some with more than one diagnosis (3,133 diagnoses in total), and found this breakdown:

• Androgenetic alopecia: 37.7% of cases
• Alopecia areata: 18.2% of cases
• Telogen effluvium: 11.3% of cases

The rest were scarring alopecias and less common types. Here's what each major cause means.

Androgenetic Alopecia (Pattern Hair Loss)

This is the most common cause of hair loss in both men and women. It's driven by genes and hormones, especially dihydrotestosterone (DHT), an androgen that gradually shrinks hair follicles until they stop producing visible hair.

According to NIH StatPearls, about 50% of Caucasian men are affected by age 50, rising to 80% by age 70. Women are also commonly affected, and rates rise noticeably after menopause. Twin studies suggest genetics account for roughly 80% of a person's predisposition, according to NIH's Endotext.

In men, it usually follows the Norwood scale: the hairline recedes at the temples, the crown thins, and the two areas eventually merge. In women, it more often appears as diffuse thinning along the part, with the front hairline usually intact.

Pattern hair loss is progressive and permanent without treatment, but it responds well when treatment starts early.

Telogen Effluvium (Shedding Triggered by Stress or Illness)

Telogen effluvium happens when a stressor pushes hair follicles out of the growth phase (anagen) and into the resting phase (telogen) too early. Shedding usually starts 2 to 3 months after the triggering event.

Common triggers include:

• Major illness, surgery, or high fever
• Childbirth (postpartum hair loss)
• Severe psychological stress
• Crash dieting or rapid weight loss
• Starting or stopping hormonal birth control
• Certain medications, such as anticonvulsants, antidepressants, and anticoagulants

Telogen effluvium is almost always reversible. Once the trigger is resolved, shedding usually stops within 3 to 6 months, and visible regrowth follows within 12 to 18 months.

Alopecia Areata (Autoimmune Hair Loss)

Alopecia areata is a chronic autoimmune condition in which the immune system attacks hair follicles. It usually causes sudden, patchy hair loss on the scalp, though it can affect any area that grows hair. In severe cases it progresses to alopecia totalis (loss of all scalp hair) or alopecia universalis (loss of all body hair).

According to NIH, the lifetime risk is about 2%, and roughly 1 in 1,000 people have it at any given time. About 34% to 50% of people with patchy hair loss recover on their own within a year, though it often comes back.

Unlike pattern hair loss, alopecia areata doesn't permanently destroy follicles, so regrowth is possible even after significant loss.

Thyroid Problems

Both an underactive thyroid (hypothyroidism) and an overactive one (hyperthyroidism) can thin the hair. Thyroid hormones help regulate the hair growth cycle, and when levels are off, follicles can enter the resting phase early.

Thyroid-related hair loss is usually spread across the whole scalp. It often reverses once thyroid levels are brought back into the normal range.

Nutritional Deficiencies

Several deficiencies are linked to hair loss:

• Iron: one of the most common reversible causes of diffuse thinning, especially in premenopausal women
• Zinc: linked to both shedding and changes in the hair shaft
• Biotin: true deficiency is rare in otherwise healthy people, and supplements show little benefit for those who already get enough, despite heavy marketing
• Protein: severe restriction, as in crash dieting, can trigger telogen effluvium

If your hair loss has no obvious cause, a clinician can order a simple blood panel to check for these before assuming it's genetic.

Medications

Many medications list hair loss as a side effect. The most common include:

• Chemotherapy drugs, which cause anagen effluvium (rapid and often complete hair loss)
• Blood thinners such as warfarin and heparin
• Beta-blockers
• Retinoids (high-dose vitamin A derivatives)
• Antidepressants and mood stabilizers
• Hormonal medications, including some birth control pills

If your hair loss started after you began a new medication, mention the timing to your prescriber. Don't stop a medication on your own.

Traction Alopecia

Traction alopecia comes from repeated tension on hair follicles, usually from tight styles such as braids, cornrows, weaves, or high ponytails worn over long periods. It most often affects the hairline and temples.

Caught early, it's reversible. After years of strain, though, follicles can scar permanently. The fix is changing how you style your hair and giving your scalp time to recover.

Which Hair Loss Treatments Are Actually Proven?

The evidence behind hair loss treatments varies widely. Some have decades of randomized controlled trial (RCT) data, some have promising early results without FDA approval, and some are heavily marketed with little reliable support. Here's where each major option stands.

FDA-Approved Treatments

Topical Minoxidil

Minoxidil is the only FDA-approved topical treatment for hair loss and is sold over the counter in 2% and 5% strengths. It lengthens the growth phase of the hair cycle and increases blood flow to follicles. It's approved for pattern hair loss in both men and women.

Results usually take 4 to 6 months to show, and you have to keep using it to keep them; hair loss returns within months of stopping. Side effects are usually mild: scalp irritation, dryness, and in some people, unwanted facial hair.

Oral Finasteride (Men Only)

Oral finasteride (1 mg daily, brand name Propecia) is FDA-approved for male pattern hair loss. It blocks 5-alpha-reductase, the enzyme that converts testosterone into DHT, the hormone that shrinks follicles. Lowering DHT slows or stops hair loss and, in many men, leads to regrowth.

In two-year clinical trials of men with mild to moderate hair loss, finasteride stopped progression in about 83% of men (vs. 28% on placebo) and produced visible regrowth in about 66% (vs. 7%). It isn't FDA-approved for women and must not be used by anyone who is or may become pregnant, because it can harm a developing fetus.

A small percentage of men experience sexual side effects, including lower libido, erectile dysfunction, and ejaculation problems. These usually go away after stopping the medication, though the FDA label notes post-marketing reports of sexual side effects that continued after stopping.

Off-Label Treatments with Strong Evidence

Low-Dose Oral Minoxidil

Low-dose oral minoxidil (usually 0.25 mg to 5 mg a day) has become one of the most promising off-label options. A 2025 meta-analysis of 27 studies and 2,933 patients, published in Frontiers in Pharmacology, found pooled rates of 47% for symptom improvement and 35% for significant improvement. Adverse events were reported in 27% of participants, most often unwanted body hair (hypertrichosis); ankle swelling (fluid retention) occurred in about 4%.

Because it's a pill, oral minoxidil avoids the daily scalp application that makes many people give up on the topical version. It isn't FDA-approved for hair loss, but many dermatologists prescribe it routinely.

Dutasteride

Dutasteride is a stronger 5-alpha-reductase inhibitor than finasteride. Finasteride blocks only the type 2 form of the enzyme; dutasteride blocks both type 1 and type 2, which lowers DHT further. Several RCTs show it increases hair density more than finasteride. It's FDA-approved for an enlarged prostate (benign prostatic hyperplasia) and prescribed off-label for hair loss. Its sexual side effect risks are similar to finasteride's.

Combination Therapy: Minoxidil Plus Finasteride

The evidence here is especially strong. A 2026 review in the Journal of Cosmetic Dermatology cites RCTs and meta-analyses on finasteride combined with topical minoxidil. The pair produced better photographic scores and more cases of marked improvement than either drug alone, without more side effects. In a separate retrospective study of 502 men taking low-dose oral minoxidil with finasteride for 12 months, 92% stayed stable or improved, and about 57% showed clear improvement.

Procedures and Add-On Treatments

Platelet-Rich Plasma (PRP)

PRP involves drawing your blood, concentrating the platelets, and injecting them into the scalp, where they release growth factors that may stimulate follicles. Several small RCTs show positive results for pattern hair loss, but study quality varies and preparation methods aren't standardized. PRP isn't FDA-approved for hair loss, and AAD clinical guidance treats it as a promising option rather than a proven stand-alone treatment. It usually takes several sessions plus maintenance injections.

Low-Level Laser Therapy (LLLT)

LLLT devices, such as laser combs and helmets, use specific wavelengths of red light to stimulate follicles. They are FDA-cleared, which is a lower bar than FDA-approved. A 2024 systematic review of 141 studies on pattern hair loss treatments appeared in the Journal of Cosmetic and Laser Therapy. It listed LLLT among the options that promote hair growth, though the effect is generally modest. It works best alongside first-line treatments rather than in place of them.

Microneedling

Microneedling makes tiny punctures in the scalp that trigger a healing response and may help topical treatments like minoxidil absorb better. Several RCTs show it improves results when combined with minoxidil compared with minoxidil alone. Evidence for microneedling by itself is more limited. It's generally well tolerated.

Ketoconazole Shampoo

Prescription ketoconazole 2% shampoo may have mild anti-androgen effects on the scalp, and small studies suggest it can modestly improve hair density. It's used off-label as an add-on, not a main treatment. The 1% over-the-counter version has less evidence for hair loss.

Hair Transplant Surgery

Hair transplant surgery is the only permanent treatment for pattern hair loss. Its two techniques, follicular unit transplantation (FUT) and follicular unit extraction (FUE), move DHT-resistant follicles from the back and sides of the scalp to thinning areas. Transplanted hair is permanent, but most people still need medical treatment to prevent further loss elsewhere. Surgery isn't appropriate for active telogen effluvium or alopecia areata.

Hair Loss Treatment Comparison: Evidence, Timeline, and Side Effects

Use this table to compare the options before talking through them with your dermatologist.

Bottom line: The strongest evidence supports topical minoxidil, oral finasteride, and the two together for pattern hair loss. Oral minoxidil is quickly becoming a common alternative or addition. Procedures work best alongside first-line medical treatment, not instead of it.

Compare prices before you fill. Prescription hair loss treatments like finasteride and oral minoxidil vary widely in price from one pharmacy to the next. Discount programs can lower your cost. Rxamined shows you the lowest available price for your prescription before you fill it.

Sources

1. American Academy of Dermatology (AAD)
2. multicenter study of 22 specialist hair clinics
3. NIH StatPearls
4. NIH StatPearls
5. according to NIH's Endotext
6. According to NIH
7. clinical trials
8. FDA label
9. published in Frontiers in Pharmacology
10. 2026 review in the Journal of Cosmetic Dermatology
11. retrospective study of 502 men
12. AAD clinical guidance
13. in the Journal of Cosmetic and Laser Therapy
14. 10-year follow-up of 118 men

This article is for informational purposes only and is not medical advice. Talk to a licensed clinician before starting, stopping or changing any treatment.