The Science Behind Curly Hair

Why is it that some people have curly hair, and some don’t? Some of it is, of course, genetic. But inheriting your hair from your parents isn’t the only reason you might have coily curls while a sibling’s hair is stick-straight.

One of the most interesting things about hair is that it’s one of the few physical attributes that we can’t permanently change. We can’t change our height either, for example, or our eye color (contact lenses don’t count)! We can temporarily change our black hairstyles and braid hairstyles with dyes, or styling products, or treatments, or heat – but the fundamentals will always remain the same. Even if you relax or perm your hair, as it grows, it will grow in the way it always was.

The genetics bit

Curly hair is what they call an autosomal dominant trait. That means that a curly-haired person inherits at least one ‘dominant’ curly-haired gene from their parents; either from their mother or their father. The curly hair gene is always expressed in a child that inherits it. So, even if you only inherit the gene from one parent (the curly-haired one), you will always have curly hair. If you don’t inherit the gene, your hair will be straight. Either way, there are still variations – depending on the strength and type of your inherited hair genes, you might end up with hair that’s wavy or somewhere in between.

How hair is constructed

How our individual hairs are constructed has a huge impact on whether it’s curly or straight. Each strand has two main elements; the shaft, and the follicle. Hair follicles live under the surface of the scalp and can’t be seen with the naked eye, but they’re super-important. It is the follicles that produce the hair shaft, and the shape of the follicle impacts the shape of the hair that grows out of it. The follicle shape is what we inherit from our parents.

hair follicles

Curly hair has really high inheritability, which means that the vast majority of what our hair texture looks like is in our DNA. People who have follicles that are symmetrical tend to have straight hair, where people who have asymmetrical follicles have curly hair. 

How the strands of hair are constructed also has an important impact on our hair texture. Curly hair tends to have unevenly-distributed keratin, a protein that makes up most of the structure of the hair. The protein component of hair is also what makes it able to be straightened or curled using heat. The heat temporarily changes the structure of the proteins that make up our hair, changing its appearance.

Caring for curly hair

Curly hair tends to be drier and more brittle than straight hair and requires specific looking after, with natural hairstyles for curly hair very popular. You can also wear your hair in a specific ‘protective’ style if you’re growing it out, and it needs to be protected from the elements. Some people also use the curly girl method to care for their hair – avoiding traditional shampoos and using conditioners, creams, and gels to wash and style.

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