Hair grows out of little pockets in your skin called follicles. There are about 5 million hair follicles on the body, including roughly 100,000 on the scalp.

Each strand of hair grows in three stages:

  • Anagen. This active growth phase of hair lasts between 2 and 8 years.
  • Catagen. This transition phase takes place when the hair stops growing, which lasts about 4 to 6 weeks
  • Telogen. The resting phase occurs when the hair is neither growing nor falling out, which lasts 2 to 3 months
  • Exogen. The shedding phase occurs when hair falls out, which can last for 2 to 5 months.

The vast majority of hair follicles on the scalp are in the anagen phase, while only 5 to 10 percent are in the telogen phase.

On other parts of the body, the process is the same, except the cycle only lasts for about a month. That’s why hair on the body is shorter than hair on the scalp.

The rate of hair growth on the head varies from person to person based on a range of factors, including ethnicity.

According to a 2016 study involving just over 2,000 young adults:

  • Asian hair grows about .49 inches (in) per month, or just under 6 in. per year.
  • Black hair grows about .33 in. per month, or just under 4 in. per year.
  • White and Latino hair grows about .44 in. per month, or 5.3 in. per year.

For example, if your hair was longer than shoulder-length, and you got a really short bob, it could take several years for your hair to grow back to the length it was before.

Keep in mind that rates of hair growth tend to decline after age 30.

Again, how long it takes for hair to grow back depends on the underlying cause of your hair loss.

Pattern hair loss

As you age, some follicles stop producing hair. This is referred to as hereditary hair loss, pattern hair loss, or androgenetic alopecia.

Many men with male pattern hair loss eventually go bald. Female pattern hair loss can cause hair to thin out, but it rarely leads to baldness.

This type of hair loss is typically permanent, which means that the hair will not grow back. But if caught early, you might be able to slow down or prevent the hair loss process with a prescription oral treatment called finasteride (Propecia), or a topical treatment called minoxidil (Rogaine).

Nutraceuticals, such as Viviscal and Nutrafol, and platelet-rich plasma therapy may also be options for early-stage pattern hair loss.

Alopecia areata

Alopecia areata is an autoimmune condition in which the immune system mistakenly attacks the hair follicles. Hair typically falls out in small patches on the scalp, but hair loss can happen on other parts of the body, such as the eyebrow, eyelashes, arms, or legs.

Alopecia areata is unpredictable. Hair may start growing back at any time, but it may fall out again. It’s not currently possible to know when it might fall out or grow back.

Scalp psoriasis

Psoriasis is an autoimmune disease that causes scaly red patches (plaques) on the skin.

Scalp psoriasis can cause temporary hair loss. Scratching at the scalp to relieve itching or to remove scales can make it much worse. Once you find an effective treatment for your psoriasis and you stop scratching your scalp, your hair will begin the growth process.

Hormonal changes

Hair loss can also happen after childbirth or during menopause due to hormonal changes.

Hair loss due to hormonal changes and imbalances is temporary, though it’s difficult to predict when the hair will start growing back.

Stress

Stress can also contribute to hair loss, whether it’s ongoing emotional stress or the result of an event, like a hospitalization, a high fever, the death of a loved one, or childbirth.

Stress-related hair loss, also called telogen effluvium, typically starts 2 to 3 months after a stressful event and can last for up to 6 months. In cases of ongoing stress, hair loss may continue for years.

Thyroid problems

Conditions that cause too much thyroid hormone (hyperthyroidism) or too little thyroid hormone (hypothyroidism) can lead to hair loss. Hair will typically grow back once the thyroid disorder is successfully treated.

Nutritional deficiencies

Not getting enough iron, biotin, or zinc in your diet can cause hair loss over time. Correcting the deficiency may lead to hair growth. Still, it can take several months for hair to start growing.

When you shave your hair, you’re only removing the top part of the hair follicle. Hair will continue to grow right away and you might start seeing stubble within a day or two.

When you wax, however, the entire hair root is removed from the follicle below the skin’s surface. It can take nearly 2 weeks before you even start to see stubble. Most people wax their hair again after 3 to 6 weeks.

Does hair grow back thicker?

You may have heard that shaving or waxing hair makes it grow back faster — and thicker. This is actually a myth. Shaving or waxing does not have any impact on how quickly hair regrows or how thick it becomes.

Chemotherapy is usually used to treat cancer. Chemo is a potent medication that attacks rapidly diving cells, such as cancer cells, but it may also attack the hair follicles in the scalp and other parts of the body, leading to rapid hair loss.

Stages of hair growth after chemo

Hair may start to regrow on its own 2 to 3 weeks after chemotherapy is completed. The hair may grow back as a soft fuzz at first. After about a month, hair may begin to grow back at its typical rate of 4 to 6 in. per year.

Keep in mind that, in some cases, it can take up to a year for hair to start growing following chemotherapy.

Your new hair may grow back a different texture or color than before. In rare instances, hair loss from many years of strong chemotherapy can be permanent.

Telogen effluvium occurs when a large number of hair follicles on the scalp enter the telogen (resting) phase of the growth cycle at the same time, but the next growth phase doesn’t start. Hair starts to fall out all over the scalp, but new hair doesn’t grow.

It’s usually triggered by a medical event, like:

Telogen effluvium usually starts about 3 months after the event. Hair may appear thin, but you likely won’t go completely bald.

This condition is fully reversible. Once the triggering event is treated (or you recover from your illness), your hair may start growing back after 6 months. However, this type of hair loss can last for years in some people.

If you’ve experienced hair loss, and you’re trying to grow your hair back, many factors can affect the rate of hair growth, including:

  • genetics
  • changes in hormones
  • nutritional deficiencies
  • medications
  • stress and anxiety
  • other diseases or conditions

You can’t always control these factors. Your best bet is to eat a balanced diet and drink plenty of water.

There’s no surefire way to make your hair grow faster overnight. But with a bit of care, you may be able to reduce certain types of hair loss or strengthen your hair to minimize breakage.

Here are some tips for keeping your hair healthy:

  • Eat a balanced diet. Aim for foods high in protein, iron, and vitamin C.
  • Ask your healthcare professional about taking supplements, particularly iron, folic acid, biotin, omega-3 and omega-6 fatty acids, and zinc — but only if you think these are lacking from your diet. There’s no need to take supplements if you’re already getting the nutrients you need from food.
  • Avoid harsh chemicals or excessive heat on your hair and skin.
  • Don’t wear tight hairstyles.
  • Give yourself a scalp massage when you wash your hair to encourage blood flow to the hair follicles.
  • Use a sulfate-free shampoo and conditioner with vitamin E or keratin. For scalp psoriasis, a dermatologist can prescribe a medicated shampoo.
  • Remove split ends with a regular trim every 6 to 8 weeks.
  • Try a topical ointment, such as topical minoxidil (Rogaine).
  • Limit or quit smoking. Quitting can be difficult, but a doctor can help you create a cessation plan right for you.
  • Protect your hair from excessive sun exposure by wearing a hat.

If you want more options in the meantime, you can use a wig or hair extensions. Hair transplants may be another option for permanent hair loss.

Hair grows back at a rate of about 6 inches per year. If your hair is falling out, talk with a healthcare professional so they can diagnose the cause of your hair loss.

If your hair loss is caused by a medical condition, you’ll need treatment to address the full condition — not just its symptoms — before the hair can recover.