The Science Behind Your Hair: What Makes Your Hair Straight or Curly?

Physically, everyone is unique. We’re different heights, have different eye colors, bone structures, freckles, and other individual differences (like that stunted, crooked left pinky or that weird lump on your ankle that your doctor swears is no problem, really). For the most part, we have our genes to thank for these differences, and your hair is no exception – but there are other factors, too. Like most realms of science, the reasons behind why your hair is straight or curly are complicated and varied. So we’ll break it down for you and so you understand why your hair is the way that it is, and give you tips for how to best care for your specific type of hair.

What Makes Your Hair Straight vs Curly

Genetics

Remember those gene charts in high school biology class, where you cross the genes of your parents in a 2×2 grid, to see which one is dominant and recessive? No? That’s ok, here’s the gist of it:

Most physical traits are either dominant or recessive, and the combination of genes from your parents determines what your physical trait will be. A mother and father, both with brown eyes, can both carry the recessive gene for blue eyes, and if the genes match up in just the right way, their son can have shiny blue eyes. Pretty cool! 

The same thing works for curly hair and straight hair. And because of the nature of recessive and dominant genes, this means that curly-haired you and your curly-haired wife could very well have a daughter with hair straighter than a spear. It all depends on which genes get passed on, and how they match up.

Studies have shown that around 85% (or sometimes more) of hair type is the result of your genetic makeup. So then what’s the other 15%?

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Angle of the Follicles

Most of it has to do with genes, but some of it has to do with angles. Angles of the follicle, in particular. 

Hair follicles are organs found in the skin, made up of multiple different types of cells, that produce hair. Think of it like the single root of a tree, that produces the hair and pushes it through the ground (skin) and into the world. 

Hair Composition

Another contributor to those straight-flowing locks is the composition of your hair. Hair is mostly composed of keratin, a hard, fibrous protein produced in the follicles. Turns out, curliness is the direct result of the keratin’s symmetry (or lack thereof).

The way I make sense of it is thinking of it like a rope. If the woven threads of a rope are thicker on one side, or bunched together in a section, that rope isn’t likely to lay straight. In hair terms, if the keratin is similarly asymmetrical, the hair is more likely to be curly. If the keratin is symmetrical (like a brand new, evenly threaded rope), the hair is more likely to be straight. And if it’s somewhere in between, well, you’re probably going to have more wavy hair. Makes sense, right?

Caring for Your Head of Hair

You know the natural state of your hair, and now you know why that’s it’s natural state. But do you know how to care for it? 

For all hair types, here’s an easy place to start: you should avoid the harsh chemical ingredients commonly found in big-poo products and treat your hair right by choosing quality products with natural, nourishing ingredients instead. Nourishing your body with a healthy diet can also help to nourish your hair. But when it comes to curly vs straight, there are some additional nuances for how to best care for your type of hair.

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How to Take Care of Straight Hair

Because of the way it grows out of the follicles and lays flat, straight hair (especially fine, straight hair) tends to become greasier more quickly. Even so, you should do your best not to wash your hair every day —too much shampooing strips your hair of the natural oils that keep it, and your scalp, healthy and can lead to more grease and dryness over time. 

With hair as straight as your granddaddy’s shotgun, washing it every other day is a safe bet. But we’re all different, so you’ll need to find your own sweet spot. Too greasy and sweaty? An extra wash every once in a while won’t hurt. To get an extra day or two out of your wash, try combing or brushing your hair once or twice a day- this can help the oils disperse more evenly throughout your strands, instead of sitting only at your roots.

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Too dry? Maybe forget the shampoo for an extra day or two and throw in some extra conditioner. 

How to Take Care of Curly Hair

Just like with straight hair, you don’t want to shampoo curly (or thick) hair every day. Lucky for you, this can be a lot easier to do for curly-haired guys since you usually have the opposite problem: instead of getting greasy, curly hair tends to get really dry. You want to let those natural oils from your hair do their thing, so a good starting place is to wash your hair every 3 days. 

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Frizz is also a common concern for curly hair – especially in the summer heat. If the mad scientist/baby bird look isn’t your jam, you’ll want to keep more moisture in your hair—which means you need to use that conditioner frequently. Even on days that you don’t shampoo your hair, you can rinse with conditioner and even put some extra conditioner in your damp hair to leave in after you shower. You can also use some products with natural hydrating oils in your hair after you rinse for those especially frizzy days.

About the Author: Jonathan Littauer

Jonathan is a freelance writer and rock climbing routesetter based in Boston, MA. He was the managing editor of Philly Current Magazine for two and a half years. And he just finished writing his first book!

When he’s not wielding words or making people fall off walls, he’s probably outside somewhere, hiking or climbing or surfing poorly. He’s been known, on occasion, to peace out and travel the world for months at a time.

Check out more of Jonathan’s work.