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January 15, 2024

Here’s how hormones and chemotherapy can change your hair

Changes around puberty and pregnancy can affect the function of genes influencing hair shape. And chemotherapy can cause hair to regrow in a different shape for the first few cycles of hair regrowth

Head hair comes in many colours, shapes and sizes, and hairstyles are often an expression of personal style or cultural identity.

determine our hair texture, thickness and colour. But some people’s hair changes around the time of puberty, pregnancy or after chemotherapy.

So, what can cause hair to become curlier, thicker, thinner or grey?

Curly or straight? How hair follicle shape plays a role

Hair is made of , a strong and insoluble protein. Each hair strand grows from its own that extends deep into the skin.

Curly hair forms due to asymmetry of both the in the hair.

Follicles that produce are asymmetrical and curved and lie at an angle to the surface of the skin. This kinks the hair as it first grows.

The asymmetry of the hair follicle also causes the keratin to bunch up on one side of the hair strand. This pulls parts of the hair strand closer together into a curl, which maintains the curl as the hair continues to grow.

Follicles that are symmetrical, round and perpendicular to the skin surface produce straight hair.

Life changes, hair changes

Our hair undergoes repeated cycles throughout life, with different stages of growth and loss.

Each hair follicle contains stem cells, which multiply and .

Head hairs spend most of their time in , which can last for several years. This is why head hair can grow so long.

Let’s look at the life of a single hair strand. After the growth phase is a transitional phase of about two weeks, where the hair strand stops growing. This is followed by a resting phase where the hair remains in the follicle for a few months before it .

The hair follicle and the stems cells grow a new hair to repeat the cycle.

Each hair on the scalp is replaced .

Hormone changes during and after pregnancy alter the usual hair cycle

Many women notice their hair is .

During pregnancy, high levels of prolong the resting phase of the hair cycle. This means the hair , with less hair loss.

A drop in hormones a few months after delivery causes increased hair loss. This is due to all the hairs that remained in the resting phase during pregnancy falling out in a fairly synchronised way.

Hair can change around puberty, pregnancy or after chemotherapy

This is related to the genetics of hair shape, which is an example of .

Incomplete dominance is when there is a middle version of a trait. For hair, we have curly hair and straight hair genes. But when someone has one curly hair gene and one straight hair gene, they can have wavy hair.

Hormonal changes that occur around and can affect the function of genes. This can cause the curly hair gene of someone with wavy hair to become more active. This can change their hair from wavy to curly.

Researchers have identified that activating specific genes can change hair in pigs .

has very visible effects on hair. Chemotherapy kills rapidly dividing cells, , which causes hair loss. Chemotherapy can also have that influence hair follicle shape. This can cause hair to for the first few cycles of hair regrowth.

Hormonal changes as we age also affect our hair

Throughout life, are essential for production of keratin. Low levels of thyroid hormones can cause dry and brittle hair.

also regulate hair growth and loss, particularly as we age.

Balding in males is due to . In particular, high dihydrotestosterone (sometimes shortened to DHT), which is produced in the body from testosterone, has a role in .

Some women experience . This is caused by a combination of genetic factors plus lower levels of after menopause. The hair follicles become smaller and smaller until they no longer produce hairs.

Reduced function of the cells that produce (the pigment that gives our hair colour) is what causes greying.

, Associate professor of Medical Sciences,

This article is republished from under a Creative Commons license. Read the .

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