Understanding how hair grows makes it easier to understand why it thins and how treatments work. This guide is a short primer on the science behind hair growth and hair loss.
The hair follicle
Each hair grows from a follicle in the skin. At its base, the dermal papilla sends signals that control growth. The scalp has around 100,000 follicles on average, and each works on its own cycle.
The hair growth cycle
- Anagen (growth): lasts years on the scalp and determines how long hair can grow. Most scalp hairs are in this phase at any time.
- Catagen (transition): a short phase when growth stops.
- Telogen (rest): the hair rests for a few months, then sheds as a new hair begins to grow.
Scalp hair grows around a centimeter a month, which is why changes in hair take months to show.
Why hair thins
- Pattern hair loss: in sensitive follicles, DHT causes gradual shrinking (miniaturization), producing thinner, shorter hairs. See DHT and hair loss.
- Telogen effluvium: a trigger pushes many hairs into the resting phase at once, causing shedding months later. See telogen effluvium.
- Autoimmune and inflammatory conditions, such as alopecia areata and scarring alopecias.
- Breakage and traction from styling and tension.
How treatments target these processes
- DHT blockers and anti-androgens reduce the hormonal signal that drives miniaturization.
- Minoxidil is thought to prolong the growth phase and affect blood flow around the follicle.
- Correcting underlying causes, such as iron deficiency or thyroid problems, removes triggers for shedding.
See treatments with the strongest evidence.
Next step
If you want a licensed provider to review your hair loss, start your online consultation.
Prescription required for prescription treatment. A licensed provider decides whether treatment is appropriate. Individual results vary. Prescribed Essence currently serves patients in California, Colorado, Florida and New York.
