Androgenetic Alopecia (Pattern Hair Loss)

How pattern hair loss happens

Each hair follicle cycles through growth (anagen, lasting years on the scalp), a short transition, and rest and shedding (telogen). In androgenetic alopecia:

1. DHT, made from testosterone by the enzyme 5-alpha-reductase, binds to androgen receptors in genetically susceptible follicles.
2. The growth phase shortens with each cycle.
3. Follicles shrink (miniaturization), producing finer, shorter, lighter hairs until some stop producing visible hair.

Many genes contribute, from both sides of the family, including the androgen receptor gene on the X chromosome. In women, the role of androgens is less clear, and many have normal hormone levels.

Signs and stages

Men

Hair loss usually starts in the 20s or 30s, sometimes in the teens:

• receding hairline at the temples (an M shape)
• thinning at the crown (vertex)
• the areas gradually merge, leaving hair at the back and sides

Doctors grade it with the Norwood-Hamilton scale (stages 1 to 7).

Women

Female pattern hair loss usually becomes noticeable after menopause but can start in the 20s:

• diffuse thinning over the top of the scalp
• a widening center part, sometimes with a "Christmas tree" pattern of thinning at the front
• the frontal hairline usually stays intact
• complete baldness is rare

It is graded with the Ludwig or Sinclair scales.

Androgenetic alopecia vs other hair loss

Androgenetic alopecia and telogen effluvium often occur together, especially in women. See alopecia for an overview.

Diagnosis

Diagnosis is usually clinical. A doctor or dermatologist will:

• ask about onset, family history, shedding, medicines, diet, illness and periods
• examine the pattern and look closely at the scalp with a dermatoscope (trichoscopy), which shows hairs of varying thickness
• in women, check for signs of excess androgens such as acne, hirsutism and irregular periods, which suggest polycystic ovary syndrome

Blood tests are not needed for typical male pattern loss. In women, tests often include ferritin (iron stores), thyroid function, and, if there are signs of androgen excess, testosterone and other hormones. A scalp biopsy is rarely needed.

Treatment

Treatments work best when started early and must be continued: stopping leads to loss of regained hair within months. Expect at least 6 to 12 months before judging results.

Minoxidil

• Topical minoxidil (5% foam or solution for men, 2% or 5% for women) is available over the counter. It prolongs the growth phase. Shedding can increase for the first 2 to 8 weeks, which is a sign it is working.
• Low-dose oral minoxidil is increasingly prescribed off-label for men and women. It can cause unwanted hair growth elsewhere, ankle swelling and fast heartbeat, so it needs medical supervision.

Finasteride and dutasteride (men)

Finasteride blocks the conversion of testosterone to DHT. It stops progression in most men and regrows some hair in many. Side effects such as reduced libido or erectile problems affect a small minority. It is not used in women who could become pregnant because it can affect a male fetus. Dutasteride is a stronger option used off-label. A topical finasteride is also available.

Women

• Spironolactone, an anti-androgen, is often prescribed, especially with signs of androgen excess. It requires reliable contraception.
• Correcting iron deficiency or thyroid problems helps if present.

Other options

• Platelet-rich plasma (PRP) injections: some evidence of benefit.
• Low-level laser devices: modest evidence.
• Hair transplant: moves resistant follicles from the back of the scalp to thinning areas. Best for stable, well-defined loss.
• Cosmetic options: hair fibers, styling, hairpieces, scalp micropigmentation.

Outlook

Androgenetic alopecia is progressive but not harmful to physical health. The rate varies widely. Treatment can stabilize it in most people and improve density in many. The psychological impact can be significant, and it is reasonable to seek treatment for that reason.

Frequently asked questions

What causes androgenetic alopecia?

It is caused by an inherited sensitivity of scalp hair follicles to androgen hormones, mainly DHT. Over time, affected follicles shrink and produce thinner, shorter hairs. Genes from both parents contribute, so it can be inherited from either side of the family.

Can androgenetic alopecia be reversed?

Partly. Treatments such as minoxidil and finasteride can stop further loss in most people and regrow some hair, especially in areas that have thinned recently. Follicles that have been inactive for many years are unlikely to recover. Hair transplant can restore density.

Does female pattern hair loss mean my hormones are abnormal?

Not necessarily. Many women with pattern hair loss have normal hormone levels. Blood tests are recommended if you also have irregular periods, acne or excess hair growth, which may point to polycystic ovary syndrome or another cause of high androgens.

How long does minoxidil take to work?

Most people see reduced shedding within 2 to 4 months, and visible regrowth after 6 to 12 months. A temporary increase in shedding in the first weeks is common. Continue for at least a year before judging the result.

Is pattern hair loss caused by stress or hats?

No. Wearing hats, frequent washing and normal styling do not cause androgenetic alopecia. Stress can trigger telogen effluvium, a temporary shedding that can make pattern thinning more noticeable.