Everyone has a hair shape. Whether straight, wavy, curly or kinky, your hair takes on a distinct pattern that remains every day. But have you ever wondered how hair gets its shape to begin with and why that texture might change over time? These things aren’t random—they have a lot to do with genetics and the chemical structure of hair.

There are a few things that can alter hair shape and texture, but most of these are temporary, such as using a hot tool or getting your hair wet. There are a few factors at play when it comes to how your hair grows out of your head in a straight or curly texture.

How hair gets its shape

One of the most prominent things that determines hair texture is the shape of your follicles—the place on the scalp where hair grows from. A round follicle is likely to produce a straight strand of hair, while a flattened or oval-shaped follicle is more likely to produce curly hair. A very flat follicle shape is likely to produce kinky hair.

The shape of your follicles is initially determined by genetics, so if both your parents have curly hair, you’re likely to have it too!

In addition to the shape of the follicle itself, the angle of the follicle under the skin can determine hair shape. While hair shafts from round follicles tend to emerge straight out of the head, oval follicles tend to push hair out of the scalp at an angle, which contributes to more curling.

Beyond this, the chemical makeup of your hair shaft comes into play, as well. The shaft of your hair is made of a flexible protein called keratin. Keratin contains amino acids—one of which is cysteine, which contains sulphur chemicals that help it form strong bonds.

The way your follicle is shaped can affect how tight or loose these bonds are able to form, which ultimately determines your hair texture. The way hair grows out of flattened follicles allows bonds to form more closely together, resulting in curly hair. In straight hair, round follicles create looser, more relaxed bonds.

Can hair texture change?

For all intents and purposes, hair texture is permanent—it doesn’t change. Most people will have the same hair texture for their entire lives, unless they do something to change it.

It is possible to alter your hair’s shape both temporarily and “permanently” through hair treatments. The difference has to do with the types of chemical bonds each method targets within your hair shaft. The two main types of chemical bonds that hold your hair’s shape are hydrogen bonds and disulfide bonds.

• Hydrogen bonds: Hydrogen bonds are quite easy to break and re-form using heat or water. By applying heat or water, you can temporarily alter your hair’s shape, which is why hot tools help curl or straighten hair. However, these bonds will eventually reset and return your hair to its normal shape.
• Disulfide bonds: Disulfide bonds are much stronger bonds in the hair shaft and cannot be altered by water or heat. Instead, these bonds must be broken and re-shaped using chemicals, and this process cannot be reversed. Chemical treatments like relaxers or perms help to re-shape these bonds and create a permanent change in your hair’s texture. However, this only affects the sections of hair treated and not your follicles, so new hair that grows out will be your normal hair texture again.

Aside from using heat or chemicals to alter hair texture, some people have experienced a random change in hair texture every few years. For example, babies may be born with straight hair that turns curly over their childhood years. Women may discover that their unruly curls start to loosen into waves. Experts are still unsure as to why this might occur in some people and not others, but some believe it is related to hormones.

Women’s hair texture changes are most common around periods of major hormonal shifts, such as the start of puberty, pregnancy or menopause.

One primary cause is believed to be an increase in androgens—sex hormones that are necessary for male development but are present in both males and females. During menopause, androgen levels may increase and alter the shape of your follicles, typically causing straight hair to become curly.

Other hormones, including insulin and thyroid hormones, may also be linked to changes in hair texture. Additionally, things like chemotherapy drugs and damage from chemical treatments can impact the shape of your follicle, potentially causing changes.

If you discover your hair texture has changed in recent years, there’s no need to fret—it’s likely due to a shift in your hormones. Unless you discover significant hair loss, all you need to do is keep your hair healthy and learn to embrace your new hair!