AGA stands for androgenetic alopecia, the most common type of hair loss in both men and women. It’s a gradual, progressive thinning driven by genetics and hormones, and it affects up to 80% of men by age 80. If you’ve noticed your hair getting thinner at the temples, crown, or part line, AGA is the most likely explanation.
How AGA Causes Hair to Thin
Hair follicles go through a natural cycle of growing, resting, and shedding. In AGA, a hormone called dihydrotestosterone (DHT) disrupts that cycle. DHT is made from testosterone and is far more potent. When it binds to receptors on hair follicles, it shortens the growth phase, meaning each new hair comes in thinner and shorter than the one before. Over time, the follicle also takes longer to produce a replacement strand after the old one falls out. This process is called miniaturization, and it’s what makes AGA different from temporary shedding: the hairs don’t just fall out, they progressively shrink until some follicles stop producing visible hair altogether.
Not every follicle on your head is equally sensitive to DHT. The follicles along the sides and back of the scalp are largely resistant, which is why even advanced AGA leaves a ring of hair around the head. The follicles at the temples, crown, and frontal scalp are the vulnerable ones.
The Genetics Behind It
AGA runs in families, but the inheritance pattern isn’t as simple as one gene from one parent. The strongest genetic link identified so far involves the androgen receptor gene, which sits on the X chromosome. Research has found that a specific genetic marker on this gene (the StuI restriction site) was present in 98% of young bald men compared to about 77% of non-bald men. Shorter repeat sequences within this gene were also more common in balding men, suggesting these variations make hair follicle receptors more responsive to DHT than normal.
Because the androgen receptor gene is on the X chromosome, men inherit it from their mothers. This is why people often say baldness comes from your mother’s side, and there’s real truth to it. But AGA is polygenic, meaning multiple genes contribute. You can inherit risk factors from either parent, and having a bald father does increase your chances regardless of what your mother’s side looks like.
What Male Pattern Hair Loss Looks Like
In men, AGA follows predictable patterns classified by the Norwood scale, which has seven stages. Stage 1 is a full head of hair with no visible recession. Stage 2 shows slight recession at the temples, sometimes called a “mature hairline,” which is common and not always a sign of ongoing loss. By stage 3, recession deepens at the temples or thinning appears at the crown. Stage 4 shows more significant loss in both areas, separated by a band of hair across the top.
Stages 5 through 7 represent increasingly severe loss. At stage 5, the thinning areas at the temples and crown start merging. By stage 7, the most advanced stage, only a band of hair around the sides and back of the head remains, and even that hair is often fine and sparse. There’s also a less common variation called Norwood class A, where the hairline recedes uniformly from front to back without creating a separate bald spot at the crown.
Not everyone progresses through every stage. Some men stabilize at stage 3 and stay there for decades. Others move from early thinning to advanced loss within a few years, especially if hair loss starts before age 25.
How AGA Differs in Women
Women experience AGA differently. Rather than a receding hairline, women typically notice diffuse thinning across the top of the scalp, especially along the part line, while the frontal hairline stays intact. The thinning tends to be more spread out, which can make it harder to recognize in early stages. Women rarely progress to complete baldness in any area, but the overall volume loss can be significant.
Hormonal shifts play a role in timing. Many women first notice thinning after menopause, when estrogen levels drop and the relative influence of androgens increases. However, AGA can begin in a woman’s 20s or 30s, particularly with a strong family history.
How Doctors Diagnose AGA
A dermatologist can usually diagnose AGA based on the pattern and location of thinning alone. When the diagnosis isn’t clear cut, a technique called trichoscopy (examining the scalp with a magnifying dermatoscope) can confirm it. The hallmark finding is hair shaft thickness diversity: when more than 20% of hairs in a given area vary significantly in diameter, that’s diagnostic of AGA. This variation reflects follicles at different stages of miniaturization sitting next to each other.
In early AGA, brown pigmentation around individual follicles is visible under trichoscopy. In more advanced stages, additional signs appear, including yellow dots, tiny white dots, and areas where follicles have stopped producing hair entirely. Blood work is sometimes ordered for women to rule out thyroid problems, iron deficiency, or hormonal imbalances that can mimic or worsen AGA.
Treatment Options
AGA is progressive, so the goal of treatment is both regrowing what’s been recently lost and preventing further thinning. Starting earlier generally produces better results because miniaturized follicles can be revived, but follicles that have been dormant for years are much harder to recover.
Topical Minoxidil
Minoxidil is the most widely available treatment, sold over the counter in 2% and 5% solutions or foams. It works by increasing blood flow to follicles and extending the growth phase of the hair cycle. The 5% concentration is more effective than the 2%. Results take about four to six months to become visible, and the effects only last as long as you keep using it. Stopping minoxidil typically leads to a return of thinning within a few months.
Oral Medications
Finasteride blocks the enzyme that converts testosterone into DHT, reducing scalp DHT levels by roughly 60 to 70%. It’s the most studied prescription option for men with AGA. A meta-analysis comparing common AGA treatments found that oral finasteride and oral dutasteride (which blocks DHT even more completely) ranked among the most effective options. Dutasteride is sometimes used when finasteride alone isn’t producing enough improvement. Low-dose oral minoxidil has also gained traction as an alternative to the topical version, with some patients finding it more convenient and easier to tolerate.
Side effects are the main concern with oral treatments. A small percentage of men on finasteride report decreased libido or sexual side effects, and these resolve in most cases after stopping the medication. Dutasteride carries a similar side effect profile. Women of childbearing age cannot take finasteride or dutasteride because these drugs can cause birth defects.
Platelet-Rich Plasma (PRP)
PRP involves drawing your blood, concentrating the platelets, and injecting that concentrate into the scalp. A meta-analysis from Johns Hopkins confirmed that PRP increases both hair density and hair thickness compared to placebo. It’s typically done as a series of sessions spaced a few weeks apart, then maintained with periodic treatments. PRP works best as a complement to other treatments rather than a standalone approach, and results vary from person to person.
Hair Transplantation
Transplant surgery moves DHT-resistant follicles from the back and sides of the scalp to thinning areas. Because these follicles retain their resistance to miniaturization, the transplanted hair is permanent. Modern techniques produce natural-looking results, but transplants work best when combined with medical treatment to protect the non-transplanted hair that remains.
Factors That Can Accelerate AGA
While genetics determine your baseline susceptibility, other factors influence how quickly AGA progresses. Chronic stress can push more follicles into the resting phase, compounding the appearance of thinning. Smoking has been linked to worse outcomes, likely through reduced blood flow to the scalp. Some research has explored a connection between insulin resistance and AGA severity, with studies finding that metabolic syndrome is more commonly associated with early-onset hair loss. The relationship is still debated, but maintaining overall metabolic health is unlikely to hurt.
Nutritional deficiencies, particularly in iron, vitamin D, and zinc, don’t cause AGA on their own but can make existing thinning worse. If you’re treating AGA and not seeing results, checking for these deficiencies is a reasonable step.