On average, hair tends to grow between 0.5 and 1.7 centimeters per month. This is equivalent to around 0.2 to 0.7 inches.
This estimate comes from The Trichological Society. However, lots of different factors affect the speed of hair growth.
Males, for example, may find that their hair grows faster than that of females. Other things that influence the speed of hair growth include genetics, age, health, and pregnancy.
Bone marrow, which is the soft substance present inside the bones, is the only part of the body that grows faster than hair.
The lips, palms of the hands, and soles of the feet are the only parts of the body on which hair does not grow. The main purpose of hair is to protect the body and keep it warm.
Keep reading for more information on how hair grows and the various factors that affect the speed of its growth.
People are born with around 5 million hair follicles. These are little pockets in the skin that hair grows out of.
Around 100,000 of these follicles are on the scalp. People with oval shaped follicles have very curly hair, while those with round follicles have straight hair.
The stages of hair growth are as follows:
- Each follicle contains a hair root, which is made of cells of protein.
- As blood circulates around the body, it delivers oxygen and nutrients to the protein cells, which they need to multiply.
- As the protein cells multiply, they build hair, which pushes up through the skin.
- As the hair grows out of the skin, it passes an oil gland. This lubricates the hair with the oil it needs to stay soft and shiny.
- By the time the hair is long enough to come through the skin, it is dead. As a new hair grows underneath, it pushes the dead hair out of the skin. The hair then falls out or is shed.
Not all hair follicles are in action at the same time. Follicles on the scalp, for example, will grow hair for a few years before becoming inactive for a period. This inactive part of the hair growth cycle is called telogen.
People lose around 50–100 hairs from their body every day as part of the normal hair growth cycle.
Everyone’s hair is different, and lots of factors can influence how quickly it grows.
- Genetics: A person’s genes will dictate how quickly their hair will grow.
- Sex: Male hair grows faster than female hair.
- Age: Hair grows fastest between the ages of 15 and 30, before slowing down. Some follicles stop working altogether as people get older. This is why some people get thinner hair or go bald.
- Nutrition: Good nutrition is essential for the growth and maintenance of healthy hair.
Telogen effluvium occurs when stress prompts the hair roots to enter the telogen stage of the hair cycle too early. It can mean that as many as 70% of scalp hairs fall out within about 2 months.
People experiencing telogen effluvium often find that their hair comes out in handfuls. It is usually most noticeable on the scalp but can affect any part of the body.
Common causes of telogen effluvium include:
- high fever
- severe infection
- severe illness
- overactive or underactive thyroid gland
- not eating enough protein
Several medications can also cause telogen effluvium. These include:
- calcium channel blockers
- nonsteroidal anti-inflammatory drugs such as ibuprofen
Telogen effluvium will usually clear up on its own once a person has sought treatment for the cause. According to the American Osteopathic College of Dermatology, the amount of shedding tends to decrease over a period of around 6–8 months.
According to The Trichological Society, there is little evidence to suggest that using special shampoos or taking supplements can make hair grow any quicker.
Good nutrition is an important part of healthy hair growth. This is because the living part of the hair (the root) receives its nutrients from the blood.
Adopting a healthful diet containing fruit, vegetables, grains, and an appropriate amount of fat will promote healthy hair.
Specific foods that can promote healthy hair include:
- Fish: Fish contains essential omega-3 fatty acids, protein, vitamin B-12, and iron, all of which prevent a dry scalp and stop hair from looking dull in color.
- Dark green vegetables: These contain high levels of vitamin A and C, which help keep hair in good condition.
- Legumes: These are full of protein, which promotes hair growth and helps prevent weak and brittle hair.
- Biotin: A biotin deficiency can lead to brittle hair or hair loss. Whole grains, liver, egg yolk, soy flour, and yeast all contain biotin.
- Nuts: These are a good source of selenium, which is important for a healthy scalp. Some nuts also contain alpha-linoleic acid and zinc. These help condition the hair and prevent shedding.
- Low fat dairy products: These are good sources of calcium, which is another key component in hair growth.
Factors that can slow the rate of hair growth include:
Learn more about how vitamin D deficiency can cause hair loss here.
Everyone’s hair grows at different rates. Many factors — including genetics, sex, and age — can influence the speed of hair growth.
Hair grows out of follicles, which are small pockets inside the skin. Each follicle contains a hair root, which is made of protein cells. As the blood vessels feed the roots with oxygen and nutrients, they multiply and grow into hair.
There is little evidence to suggest that specialist shampoo or supplements can speed the rate of hair growth. Instead, eating a nutritious diet that includes plenty of protein is essential for healthy hair.