Finasteride restores Male Pattern Baldness(MPB) hair loss by blocking type-II 5 alpha reductase enzyme that causes hair follicles to shrink by increased dihydrotestosterone(DHT) and boosting the growth phase of the hair cycle called the anagen phase.

Many studies demonstrate the efficacy of finasteride to regrow hair lost from Male Pattern Baldness (MPB). In one such study:​

• Treatment with finasteride 1 mg day−1 for 48 weeks increased both total and anagen hair counts, and improved the anagen to telogen ratio.
• “Conclusions: These data provide direct evidence that finasteride 1 mg daily promotes the conversion of hairs into the anagen phase. These data support that finasteride treatment results in favorable effects on hair quality that contribute to the visible improvements in hair growth observed in treated patients.”

So What are the Anagen & Telogen Phases?

The growth of scalp hair is a cyclical process of successive phases of growth (anagen) and rest (telogen).

The growth rate varies individually and other factors – genetics, age, environmental, level of abuse using chemicals etc play a part.

Hair can grow between 0.6 to 3.36 cm per month. Growth rate of scalp hair depends on age, sex and even ethnicity. No significant difference noted in the rate of growth between men and women. On an average hair grows at a rate of 1 centimeter/month.

Each hair is in its own phase of development. After the cycle of growth and rest, the process restarts and a new strand of hair starts to grow. The three stages of hair growth are anagen catagen and telogen, a fourth phase called exogen is also identified for shedding phase.

Anagen Phase of Hair Growth

Forming the growth phase of hair. Around 90% of the hair on the head is in this phase.

The growth begins in the papilla and hair can be in this phase from 3 to 5 year. Genetics determine the length of time hair stays in this phase. This is where Finasteride helps recoup hair loss from Male Pattern Baldness (MPB).

Longer hair stays in the anagen phase, longer it will grow. In this phase, cells around the papilla divide to produce new hair, and the follicle buries into the dermal layer of the skin to nourish.

Catagen Phase of Hair Growth

This is the transitional phase where the follicle renews to start a new hair. The hair follicle shrinks and the hair is cut off with the papilla detaching. It stays in this resting phase for about two weeks.

This phase will affect about one percent of all hair of one’s body at any given time. The follicle is 1/6th of its original length, causing the hair shaft to be pushed upwards.

Telogen Phase of Hair Growth

This is the resting phase where the hair follicle remains dormant for one to three months. About ten to fifteen percent of the hair on the head is in this phase of growth at any point of time.

The epidermal cells lining the follicle continue to grow and may accumulate around the base of the hair. This helps to preserve the hair without taxing resources needed for the growth phase, which will start after this phase.

The follicle will begin to grow again, softening the base of the hair shaft first. The hair base will then break from the root which will be shed.

A new hair shaft will start growing within two weeks once the resting phase is complete. This process causes shedding of hair which is normal.

Details of the Finasteride Study

The current study used a phototrichogram methodology to assess the effect of finasteride on the phases of the hair growth cycle. Previous clinical trials in men with androgenetic alopecia, treatment with finasteride increased scalp hair counts in a defined area (i.e. increased hair density).

Two hundred and twelve men, aged 18-40 years with androgenetic alopecia or Male Pattern Baldness were randomly given finasteride 1 mg/daily or placebo for 48 weeks.

At baseline, 24 weeks and 48 weeks macro photographs were taken to measure total and anagen hair count in a target area of the scalp.

“Results At baseline, mean total and anagen hair counts in the finasteride group were 200 and 124 hairs, respectively (% anagen = 62%) and the anagen to telogen ratio was 1·74 (geometric mean). In the placebo group, the respective values were 196 and 119 hairs (% anagen = 60%) and 1·57. At week 48, the finasteride group had a net improvement (mean ± SE) compared with placebo in total and anagen hair counts of 17·3 ± 2·5 hairs (8·3% ± 1·4%) and 27·0 ± 2·9 hairs (26% ± 3·1%), respectively (P < 0·001). Furthermore, treatment with finasteride resulted in a net improvement in the anagen to telogen ratio of 47% (P < 0·001). “

In this study, treatment with finasteride 1mg day−1 for 48 weeks increased both total and anagen hair counts, and improved the anagen to telogen ratio.