The Science of Beauty: How to Take Care of Curly Hair

If you have spirals, coils, or waves, you already know that having curly hair isn't just a trait; taking care of it, is a lifestyle. While not biologically different from straight hair, curly hair comes with its own set of needs that expand or contract based on porosity (we’ll cover that), curl pattern (we’ll definitely cover that), and the products you use (yep… we’ll get to those, too). Add the fact that many folks actually have different kinds of curls growing out of different parts of their scalp, and you’ve got a recipe for confusion — and more than enough material for a full episode of The Science of Beauty podcast.

So with help of cosmetic chemist Erica Douglas, our hosts Michelle Lee, editor in chief, and Jenny Bailly, executive beauty director, set out to explain what curls actually are, debunk some common myths, and a whole lot more. Read on for the highlights.

What Makes Hair Curly?

If you put a strand of curly hair under a microscope, it won’t have any biological differences from a straight one. It’s the shape of the follicle each hair grows from that dictates how straight, curly, or coily an individual strand will be, explains Douglas on our episode. “If you have a U- or C-shaped follicle, you're going to have very curly hair,” she says, adding that follicles with a slight bend produce wavy hair and perfectly round follicles produce straight hair. In addition to follicle shape, the angle at which hair follicles tunnel into the scalp contribute to whether or not hair will curl, wave, or grow in straight. Straight hair follicles tunnel vertically into the scalp while curly and wavy follicles angle into the skin, causing the hair to curve as it grows, eventually creating curls.

The angle and shape of follicles also contributes to another distinguishing characteristic of hair: how each strand is structured. Keratin is distributed via the follicle and provides structure to human hair. In a straight-haired follicle, keratin is evenly distributed on each strand (keeping it straight), but in the U- or C-shaped follicles that produce curls and kinks, keratin accumulates more on one side of the hair strand than the other, further enhancing that spiral shape. So what dictates the shape of our follicles? It’s largely genetic.

How Are Curls Classified?

Figuring out the types of curls you have — and yes, there can be multiple — is a big part of determining which products will work best for you. Over time, a basic system of curl classification has been developed, first by stylist Andre Walker, and then built upon by online communities like Naturally Curly. These charts typically range from 2, which is wavy, through 4, which is coily. (Type 3 curls include loose spirals to tight corkscrews and type 4 hair is the most tightly coiled.) These types are additionally divided by textures: thin and fine to thick and coarse as ranked from A through C. Within these curl pattern charts, you can have any combination of texture and curl — 2B, 4C, 3A, for example..

That said, these types of curl classifications don’t necessarily make your curl-care plan cut and dried, as Douglas explains: “Some people have different curl patterns all around [their heads].” As in, you might have 3A curls on top of your head and then 4B curls at the base of your neck.

For this reason, Douglas recommends using curl pattern charts as a starting point only. When it comes to truly understanding curls and coils, other factors include porosity (we’re getting to that!), scalp health, and what you’re putting into your body—if you’re deficient in certain nutrients, for example, your hair may thin.

Can Curl Patterns Change?

In short, yup. Over time, curl patterns can become tighter or looser. Hormones, especially during pregnancy, menopause, or puberty, certain medications, and external environmental factors can all play a role in changing the shape of hair follicles which, in turn, can affect curl type and pattern.

Graying is also associated with a change in curl patterns. Around the same time hairs lose melanin — the colored pigment found in hair — follicles start producing less sebum (oil), and as a result strands become more wiry and less pliable. Because the hair is more wiry, it can be harder to align with other parts of your curl pattern.

Damage — especially heat damage — can also have a major impact on curls. The more you manipulate your hair, the more its structural integrity breaks down. Though heat-styling doesn’t affect the hair follicle itself, once damage is done to a curl, the only way to undo it is by cutting it off.

That said, Douglas points out that it’s important to remember that hair is dead by the time we see it. The only time hair is actually able to heal itself is when it’s in liquid form under the scalp. Wait, what? Yup. What you know as hair actually exists under the scalp in a different physical state: not exactly a liquid, but certainly more liquid than a strand. “It’s the aggregation of proteins and nutrients under your scalp,” explains Doulgas. “Everything that’s in our bodies kind of gets frozen in time in your hair because it’s an imprint of everything that’s in your bloodstream.” Hair becomes the hardened, strand-shape mass we see growing outside our skin through a process called keratinization, and hair is at its healthiest when it is first pushed through the scalp. In Douglas’ words, “it’s all downhill from there.”

What Is Hair Porosity?

Your hair’s porosity describes how its cuticles absorb and maintain moisture. Low porosity hair means your cuticles are compact and difficult to penetrate. High porosity hair, on the other hand, sucks up moisture like a sponge because its cuticles are lifted, often as a result of color processing or heat damage. Each level has its own pros and cons, explains Douglas. While high porosity hair is quick to absorb moisture from products, leaving it well-hydrated, it’s also quick to absorb moisture from its environment which can result in frizz. Low porosity hair, on the other hand, is slow to absorb moisture, but once it’s locked in, it’s really locked in.

Curls are more delicate than straight strands due to the shape of the hair fiber. The spiral shapes means the cuticle can be slightly lifted, which makes it more prone to damage, and more likely to leak moisture. Because of this, curls tend to become damaged and dehydrated far more quickly than straight hair.

A great way to figure out your hair’s porosity is through a simple test that involves placing a strand of hair in a glass of water and watching how the hair reacts. “If [your hair] floats for a very long time, that is a sign you have low porosity hair,” explains Douglas. She encourages those who try this experiment to think of their hair like a boat. “In a boat, you want the bottom sealed up. That’s what makes the boat float.” But if you have high porosity hair that sinks quickly to the bottom, the cuticle is lifted and can’t keep the moisture out. “If [your hair] starts to sink immediately that’s usually a sign of high porosity hair because it’s taking on all that water.”

Curly Hair Care

In addition to its fragility, curly hair is also more prone to knots and tangles. So while it’s tempting to rake a paddle brush through knots, it’s incredibly important to handle curls with extra care.

How Should Curly Hair Be Washed?

Avoid harsh, stripping shampoos, especially those containing sulfates. Because while sulfates do a great job of cleaning hair, they’re also intense detergents. The main ingredient in sulfate-based shampoo, sodium lauryl sulfate, can lift the hair’s cuticle — which, as we know, is extra-delicate in spirals — and that can rob curly hair of the moisture it so desperately needs to stay healthy. As an alternative to sulfate-based shampoos, many members of the curly and natural hair communities co-wash their hair. This technique is exactly what it sounds like: using conditioner instead of shampoo to break down and rinse build off of the scalp and hair. You can use any conditioner to do this (though you may want to mix in the tiniest bit of shampoo to help cleanse), but co-washes marketed as such typically contain a small amount of ultra-gentle cleansing agents.

How Should Curls Be Conditioned?

The short answer is: deeply. The long answer is that in addition to having a harder time retaining moisture, curls also struggle to receive the natural moisture created by the body. Hair follicles produce an oil called sebum, Douglas explains, but it has a harder time traveling down the curved shafts of curls and coils. (This explains why the ends of curly hair tend to get particularly dry.) So regular, deep conditioning is recommended for curly hair, especially on the lengths and ends. Products with shea, cocoa, and murumuru butters keep curls soft and hydrated.

How Else Can Curls Be Protected?

While everyone’s curls are different, the overwhelming majority of experts recommend applying styling products to sopping wet curls to avoid frizz and that stiff, sticky feeling that can come from applying products to damp or mostly dried hair.

Douglas also said on our episode that it really is worth using a silk pillowcase or wearing a bonnet while you sleep, as traditional cotton pillowcases soak up the moisture your hair needs. Plus, silk results in less friction, which can create frizz. For the same reason, steer clear of rough-drying your hair with traditional towels. Instead, gently blot curls dry with a microfiber towel or t-shirt.

How Does Heat Styling Affect Curly Hair?

Extended exposure to high levels of heat is just about the worst thing you can do to curly hair. That’s because heat alters the proteins that lock curls in their spiral shape. During our episode, Douglas explains that heat rushes through the tiny cracks on the surface of the cuticle, causing abrasions to spread. “It’s almost like if you threw something really hard at a window and it starts to crack,” she says. “...and you see all the little hairline cracks going through the window.” Since curls are already fragile by nature, if heat is applied regularly, this can have serious long term ramifications. Some experts recommend limiting blow-drying to twice a week max and never using hot tools at above 400 degrees fahrenheit.

A great option for heat-styling curls while causing less damage is using a diffuser, which attaches to a blowdryer and allows for more even heat distribution, adds Douglas, who strongly recommends using a heat protectant — and even suggests trying one with an ingredient that’s a bit taboo in the curly hair community. “I know a lot of curly girls don't like the word silicone, but silicones are really great at protecting your hair from heat because they slow down how fast the heat [travels] through the cuticle,” she explains.

How Can Curls be Chemically Straightened?

There’s no way to chemically straighten hair without sustaining some kind of damage. (This also works the opposite way: there’s no way to make straight hair curl without sustaining some damage, as well.) There are two major ways to chemically straighten curls: relaxing, which is a permanent straightening process, and keratin treatments, which are a semi-permanent procedure and don’t actually have much to do with keratin at all.

Relaxers are thick creams that usually contain high levels of sodium hydroxide, which Douglas says “essentially goes through the cuticle layer and rearranges the disulfide bonds in the hair.” Disulfide bonds are what lock in the shape of our hair once it’s sprouted from the follicle, but can be broken down and manipulated by very high pH ingredients like sodium hydroxide. The heavy texture of relaxers smooth out curls while the sodium hydroxide breaks those disulfide bonds so the hair is permanently locked into a different, straighter form. Relaxing hair chemically is fast and effective, but hair that’s relaxed consistently will eventually break due to weakened cuticles.

Traditional keratin straightening treatments, by contrast, infuse hair with formaldehyde-derived ingredients such as methylene glycol which — when paired with extreme heat such as flat ironing or blow-drying — bond the chemicals to the proteins within the hair. This treatment can superficially straighten hair for up to three months, but it will eventually wash away. It’s worth noting that when the ingredients in these treatments are heated or mixed with water, formaldehyde, a carcinogen which can be dangerous to inhale, is released. Recently, though, many formaldehyde-free alternatives have become available. These use glyoxylic acid or a derivative to achieve a similar smoothing effect.

Faux Curls

The grass is always greener, right? Here’s how to create the curls of your dreams even if you’ve got naturally straight hair. Just remember, changing the shape of your hair — whether temporarily with heat or permanently with chemicals — requires the bonds in your hair to be compromised, thus creating damage. So proceed with caution.

How Do You Create Faux Curls?

Remember those disulfide bonds we said determine the shape of your hair once it’s grown out of your head? These bonds can be temporarily broken by heat, allowing hair to be rearranged into new structures that stay in place as they cool, taking it from straight to curly and vice versa.

When it comes to getting straight hair to hold a curl, there are a number of factors that can cause the operation to fall flat. These include using thick products that can make hair stringy, or applying any product at the wrong time. The best time to apply products to hair you’re planning on curling is the same as with natural curls: when the hair is sopping wet. While you’re at it, be sure to distribute the product evenly.

But if it’s humid or rainy out, you might want to reconsider your game plan. As Douglas explains, heat-styling works, in part, by breaking hydrogen bonds — as in, the H in H20 — from the hair. “You’re literally pulling the [hydrogen] off the hair,” she says. Wet or humid weather reintroduces that hydrogen right back into strands, which means they’ll revert back to their true shape.

A more permanent alternative to heat-styling is accurately called “the perm,” which uses chemicals to break down the bonds within hair and reform them in a new shape, either straight (a relaxer) or curly. To permanently add waves or curls to straight hair, it’s usually wrapped in rods and set into its new shape before the chemical solution is applied. The bonds in the hair are then disrupted, reshaped, and neutralized, freezing the bonds in the hair into their new shape.

Our Editors’ Favorite Curly Hair Products

As much as our hosts Michelle and Jenny know about curls from working at Allure, they don’t have curly hair themselves. So they invited three colleagues — Features Director Jessica Cruel, Digital Staff Writer Nicola Dall’Asen, and Digital Editor Jihan Forbes — to share the products that put a spring in their curly strands.

Jessica’s Current Favorites

Jessica describes her tight curls as mostly 4B, and says the most important step in her hair routine is Philip Kingsley Elasticizer Deep-Conditioning Treatment, which helps detangle and moisturize before washing. Her first in-shower step is TPH by Taraji Never Salty scalp scrub, which she says helps hydrate dry patches and cleanse her scalp.

Once she’s out of the shower, Jessica uses Mielle Organics Avocado Moisturizing Hair Milk (which leaves her hair feeling “so soft”) along with the Tangle Teezer brush. And last but not least, her favorite styling product is African Pride Moisture Miracle Shea Butter & Flaxseed Oil Curling Cream. “I layer that on and twist my hair into two strand twists,” she says.

Philip Kingsley Elasticizer Deep-Conditioning Treatment



TPH by Taraji Never Salty



Mielle Organics Avocado Moisturizing Hair Milk



Tangle Teezer The Original Detangling Hair Brush



African Pride Moisture Miracle Shea Butter & Flaxseed Oil Curling Cream



Nicola’s Current Favorites

Nicola characterizes her curls as a mix of 2B and 3A — so a combination of S-shaped waves and looser ringlets. But her hair is also super fine, so she’s always on the lookout for products that prevent her curls from falling flat. Not Your Mother's Curl Talk Frizz Control Sculpting Gel does the job without leaving her strands the least bit crunchy.

Her Aquis Original Hair Turban, made with microfiber, helps her hair dry faster and reduces frizz, she says. (Plus its size and shape makes it way easier to practice the plopping technique for drying.) That said, when she’s short on time, the diffuser attachment for the Dyson Supersonic hairdryer “prevents my hair from losing volume right away,” she says. “I just flip my head upside down and kind of scrunch the diffuser into my hair.”

Not Your Mother's Curl Talk Frizz Control Sculpting Gel



Aquis Original Hair Turban



Dyson Supersonic Hair Dryer Copper Gift Edition

$400.00, Dyson


Jihan’s Current Favorites

For her self-described mix of 3C, 4A, and 4B curls and coils, Jihan loves Ankh Rosemint Shampoo, which she says does an excellent job at dentagling. Philip Kingsley Moisture Extreme Conditioner is “truly amazing” in that it leaves her hair feeling ultra-soft. Bread Beauty Supply Hair-Wash and Kristin Ess Ultra Hydrating Curl Co-Wash are soothing, moisturizing options for when she wants to skip shampoo.

As for stylers, Jihan has been using Afro Sheen Crown Defining Curl Cream non-stop. “It makes my hair really nice and shiny,” she says. And she scrunches Beleza Natural Humectant Oils into her curls when she’s gone overboard with gel because they “take away all that crunch,” she says.

Ankh Rosemint Shampoo



Philip Kingsley Moisture Extreme Conditioner



Bread Supply Hair Wash

$20.00, Bread Beauty Supply


Kristin Ess Ultra-Hydrating Curl Co-Wash



Afro Sheen Crown Defining Curl Cream



Beleza Natural Humectant Oils



The (Abbreviated) History of Curls

Beauty trends come and go, but few have the political impact of curly hair. We’re talking way back — okay, in 1660 — when curly wigs were first worn by judges in England to make it impossible to tell who had chopped their hair short and rebelled against King Charles I.

But enough about white men hiding from the legal ramifications of their actions. Let’s chat about how curls have been coveted for centuries so much so that the first iteration of a curling iron was invented by Marcel Grateau in 1872. His invention, while worlds away from a Beachwaver, did create the first faux curls, known as the “marcel wave.” About 30 years later, Charles Nessler set one of the first ever perms. It took about six hours and allegedly featured a concoction of urine (whose urine it was, exactly, has been lost to history), sodium hydroxide, and water. In the 1940s and 1950s, curls hit the silver screen atop the heads of glamorous movie stars like Elizabeth Taylor. These curls enticed American women to start using hot rollers to style their own hair that way.

A decade or so later, women with natural curls and coils began to embrace their natural textures, as inspired by the Civil Rights Movement. This continued through the 1970s, when stars like Donna Summer and Diana Ross wore their curls and coils with pride, in turn bringing the afro to center stage. By 1983, the first salon specializing exclusively in curls was opened in NYC by a hairstylist known as Ouidad.

For the past couple of decades, the natural hair movement has been gaining even more steam. More and more women (and men) with curls and coils have been setting down their hot combs and steering clear of relaxers. That said, the fight for equal treatment of folks with curls and coils isn’t over. The CROWN Act — legislation to end discrimination based on race-based hairstyle and texture — is proof of that. But progress is being made — and one can say, almost definitively, that no other hair type or texture has such a fascinating history.

The Bottom Line

There’s no denying curly hair requires a lot of TLC. But as you begin to understand the science behind what curls actually are — and how they can change over time — it all starts to make a lot more sense why.

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Originally Appeared on Allure