Our hair grows because of a process called follicular cycling. Follicular cycling is made up of three phases: anagen, catagen, and telogen.

• Anagen: The anagen phase is the growth phase. During this phase, the hair follicle is actively producing new hair. The anagen phase can last for years, depending on the location of the hair. For example, the anagen phase for hair on the scalp can last for 3 to 5 years, while the anagen phase for hair on the eyebrows can last for only 1 to 3 months.
• Catagen: The catagen phase is the transition phase. During this phase, the hair follicle stops producing new hair and the hair shaft separates from the follicle. The catagen phase is a short phase that only lasts for a few weeks.
• Telogen: The telogen phase is the resting phase. During this phase, the hair shaft remains attached to the follicle but is no longer growing. The telogen phase can last for several months.

When the telogen phase ends, the hair shaft falls out and a new hair follicle begins the anagen phase.

The length of our hair is determined by the length of the anagen phase. The longer the anagen phase, the longer the hair will grow.

There are a number of factors that can affect hair growth, including:

• Genetics: Genetics plays a major role in hair growth. Some people are genetically programmed to have thicker, longer hair than others.
• Hormones: Hormones, such as testosterone and estrogen, can also affect hair growth. For example, men typically have thicker, longer hair than women because of the higher levels of testosterone.
• Nutrition: A healthy diet that is rich in protein and vitamins can help to promote hair growth.
• Stress: Stress can also affect hair growth. When we are stressed, our bodies produce more cortisol, a hormone that can damage hair follicles.
• Medical conditions: Some medical conditions, such as alopecia areata, can also cause hair loss.

If you are concerned about your hair growth, it is important to see a doctor or dermatologist. They can help to determine the cause of your hair loss and recommend treatment options.