Hair grows out of little pockets in your skin called follicles. According to the American Academy of Dermatology, 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 two and eight years.
  • Catagen. This transition phase takes place when the hair stops growing, which lasts about four to six weeks
  • Telogen. The resting phase occurs when the hair falls out, which lasts two to three months

The vast majority of hair follicles on the scalp are in the anagen phase, while only 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. This is why hair on the body is shorter than hair on the scalp.

Age, genetics, hormones, thyroid problems, medications, and autoimmune diseases can all cause hair loss. If, and how quickly, your hair grows back after hair loss will depend on the underlying cause of your hair loss.

The hair on your head grows about a half inch per month, or 6 inches per year. In general, male hair grows slightly faster than female hair. After a bad haircut, you can expect your hair to grow back at about this rate.

If your hair was longer than shoulder-length and you got a really short bob, it can take several years to grow the hair back to where it was before.

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

Pattern hair loss

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

This type of hair loss is typically permanent, which means that the hair will not grow back. The follicle itself shrivels up and is incapable of regrowing hair. You might be able to slow down the hair loss process with a prescription oral treatment called finasteride (Propecia), or a topical treatment called minoxidil (Rogaine).

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.

Alopecia

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 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

Women may lose hair following childbirth or during menopause. Men can also lose hair due to changes in hormonal makeup as they age.

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

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 or zinc in the diet can cause hair loss over time. Correcting the deficiency may lead to hair growth. Still, it can take several months for hair to regrow.

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 two weeks before you even start to see stubble. Most people feel the need to wax their hair again after three to six weeks.

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.

Hair will start to regrow on its own two to three weeks after chemotherapy is completed. The hair may grow back as a soft fuzz at first. After about a month, real hair will begin to grow back at its normal rate of 6 inches per year.

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 childbirth, surgery, or a high fever, or starting or stopping medications, like birth control pills.

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

The condition is fully reversible. Once the triggering event is treated (or you recover from your illness), your hair may start growing back after six 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 healthy, well-balanced diet and drink plenty of water.

There’s no surefire way to make your hair grow faster overnight. You should try to keep your hair as healthy as possible to prevent breakage as your hair goes through its natural growth stages.

Tips for keeping your hair healthy include:

  1. Eat a well-balanced diet. In particular, foods high in protein, iron, and vitamin C; hair is made almost entirely of protein and consuming enough is important for hair growth.
  2. Ask a doctor 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.
  3. Avoid harsh chemicals or excessive heat on hair and skin.
  4. Don’t use tight ponytails or braids.
  5. Give yourself a scalp massage when you wash your hair to encourage blood flow to the hair follicles.
  6. Use a shampoo and conditioner with vitamin E or keratin; for scalp psoriasis, a dermatologist can prescribe a medicated shampoo.
  7. Remove split ends with a regular trim every six to eight weeks.
  8. Try a topical ointment, such as topical minoxidil (Rogaine).
  9. Don’t smoke. Quitting can be difficult but a doctor can help you create a cessation plan right for you.
  10. Protect your hair from excessive sun exposure by wearing a hat.

As you take steps to support hair regrowth, consider using a wig or hair extensions in the meantime. Hair transplants may be another option for permanent hair loss. But you should do what makes you happy. Neither option is necessary.

Hair grows back at a rate of about 6 inches per year. If your hair is falling out, visit a doctor so that 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.