Hair grows in four distinct stages. The final stage involves the shedding of old hair, making room for new hair growth. Certain conditions can disrupt the stages of hair growth.

The growth and loss of hair may seem like a simple process, but the hair growth cycle is actually composed of four distinct phases. These stages of hair growth have been studied in great depth to better understand how hair grows and what might be done to prevent or treat premature hair loss.

The first three phases — anagen, catagen, and telogen — cover the growth and maturation of hair and the activity of the hair follicles that produce individual hairs. During the final, or exogen, phase, “old” hair sheds, though usually, a new hair is getting ready to take its place.

Each phase has its own timeline, which can be affected by age, nutrition, and overall health. That means there are steps you can take along the way to help ensure that your hair follows a healthy growth cycle. Read on to learn more.

The stages of hair growth begin with the anagen phase. It’s the longest phase, lasting about 3 to 5 years for the hairs on your head, though for some people a single hair could continue growing for 7 or more years.

Fortunately, the anagen phase differs with different types of hair. For example, the anagen phase for eyebrow hairs and pubic hairs is much shorter than the phase for your scalp hairs.

During the anagen phase, your hair follicles are pushing out hairs that will continue to grow until they’re cut or until they reach the end of their lifespan and fall out. At any time, about 90 percent of the hairs on your head are in the anagen phase.

The catagen phase starts when the anagen phase ends, and tends to last about 10 days or so. During this chapter, hair follicles shrink and hair growth slows. The hair also separates from the bottom of the hair follicle, yet remains in place during its final days of growing.

Only about 5 percent of the hairs on your head are in the catagen phase at any given time.

The telogen phase typically lasts around 3 months. An estimated 10 to 15 percent of your scalp hairs are in this phase.

Hairs don’t grow during the telogen phase, but they don’t usually fall out either. The telogen phase is also when new hairs start to form in follicles that have just released hairs during the catagen phase.

Some health experts consider the telogen phase the shedding phase, as well, but many scientists have divided this stage into two parts: the telogen and exogen stages.

The exogen phase is essentially an extension or a part of the telogen stage of hair growth. During the exogen phase, hair is shed from the scalp, often helped along by washing and brushing. Losing 50 to 100 hairs per day during the exogen phase is normal.

During the exogen phase, which can last about 2 to 5 months, new hairs are growing in the follicles as old hairs fall away.

Having healthy, fuller hair depends on genetics and hormone levels, which are largely beyond your control, as well as manageable factors related to a healthy lifestyle and proper hair care. Some of the best strategies for all four stages include:

Good nutrition

Because hair is largely made of protein, you should keep up your protein intake by focusing on healthy proteins. That includes:

  • lean meats
  • fish
  • beans
  • legumes
  • low-fat dairy products

A 2019 study in the journal Dermatology and Therapy also found that sufficient intake of the following nutrients was associated with healthy hair growth:

Zinc, folic acid, and vitamin B12 may also be associated with promoting healthy hair growth.

Reduced stress

The Mayo Clinic reports three different premature hair-loss conditions related to high stress levels. They include:

  • Telogen effluvium. This condition accelerates hair from the anagen phase into the telogen phase and then into the exogen phase, doubling or tripling normal daily hair loss
  • Trichotillomania. This psychological condition causes an irresistible urge to pull hair from your scalp or other areas of your body
  • Alopecia areata. This condition occurs when the body’s immune system attacks healthy hair follicles, causing hair loss

Learning to de-stress with the help of yoga, meditation, breathing techniques, counseling, and avoiding some of the daily stressors in your life may help reduce your stress, which can have many positive health benefits.

Proper hair care

Healthy hair care starts with choosing the right shampoo. Look for products designed for your type of hair, whether it’s oily, dry, fine, color-treated, etc.

The right conditioner can also make a difference, but finding the right products may take some trial and error. Pay attention to how your hair responds to various shampoos and conditioners.

Treating your hair gently is also important to promoting healthy growth. Avoid very hot water when you shampoo and towel-dry your hair gently when you’re done. Hair is more vulnerable to damage when it’s wet. Turning down the heat when drying your hair may also make a difference.

The four phases of hair growth include anagen, catagen, telogen, and exogen. Each phase lasts for a different length of time.

A healthy lifestyle of low stress, proper diet, and gentle hair care should help promote healthy hair growth for a long time.

If you believe that you’re losing your hair at a faster rate than you’re used to, talk with a doctor. An underlying condition that’s disrupting the stages of hair growth may be to blame, and treating it promptly may help slow hair loss and preserve the healthy hair you have left.