How does rogaine (minoxidil) work to cause hair growth?

No one knows: Rogaine (generic name: minoxidil) was first used as an oral drug for high blood pressure. One of it's side effects was that it also caused increased growth of fine body hairs, or in some cases, significant hair growth. The company made it a topical solution which stimulated hair growth and marketed it as rogaine. The exact mechanism of action for hair growth is unknown.

According to them: "the exact mechanism of action of rogaine (minoxidil) is uncertain. However, researchers believe that rogaine (minoxidil) works in part by partially enlarging the hair follicles and reversing the miniaturization process. By enlarging miniaturized follicles, the growth phase of the hair cycle is prolonged, allowing the hair to become longer and thicker looking and with more follicles in the growth phase at the same time.".

Funny story: Rogaine (minoxidil) was originally developed as a blood pressure medicine. Ineffective for blood pressure, it did cause excessive hair growth as a side effect. That lead to a whole new life for this failed blood pressure medicine. It is believed that rogaine (minoxidil) works by shortening the follicle telogen, stimulating hair growth. Another theory is that it dilates the follicle blood capillaries causing hair growth.

Increases blood flow: Minoxidil, the active agent in minoxidil, causes vasodilation of the capillaries to increase blood flow to the skin where it is applied.