How does hair straightening actually work?

Have you ever been straightening your hair and wondered exactly what is happening? Or why when it rains, all your hard work goes to waste?

Maybe this has never crossed your mind because you’re already running late, or you’re too worried about burning your hair, or losing a finger. Concerns I completely understand.

But as a creature of science, I started to wonder what exactly this extremely hot pair of tongs was doing to my hair.

Science in action. Hopefully she’s using a heat protectant. Source: Flickr

Bonding time

I did a little research and it turns out that when you apply heat to your hair, it breaks apart the hydrogen bonds in your hair. While this sounds scary, this actually happens every time we wet our hair. So, there’s no need to worry, you’re not damaging your hair (that’s not to say heating your hair is healthy).

As your hair dries or cools, these hydrogen bonds start to reform and they take on whatever shape your hair is in.

This is why technique can make all the difference when we curl, straighten and blow-dry our hair.

For example, after curling a section of hair, if you pin it up or put it in a bun (my lazy alternative), you are allowing the hair to cool in a curled shape which allows all of the hydrogen bonds to reform in this pattern. Similarly, when you straighten your hair, it’s best to pull a section taught and slowly move the heat plates over that section once. This both reduces heat damage, and allows the hair to cool in a straight texture.

If the bonds break when our hair gets wet, does this mean we can use water to style out hair?

Yes! If you’ve ever gone to bed with wet hair in braids, you would’ve noticed that you had very curly hair in the morning. The exact same thing is happening here – as the hair dries, the hydrogen bonds reform in the shape of the braid.


Is straightening really bad for your hair?

Heat styling isn’t great for your hair, and it’s certainly not the best option if you want to keep your hair in pristine condition. But, there are ways to do it right.

The thing that will make your hair appear dry, and dull is if you damage your cuticle. More worrying, is that if you damage your cuticle, you’re more likely to damage your cortex which will affect your hair’s strength, resistance to breakage, elasticity and colour. These hydrogen bonds we talked about above can be permanently damaged, so you have to be careful.

We need to back-track a bit to understand this.


Wait, what is the cuticle and cortex??

So, basically, your hair has three layers: the cuticle, cortex and medulla.

Your cuticle is the outer-most layer and its made up of lots of little overlapping scales – up close it kind of looks like snake skin. The function of the cuticle is to protect the inner layer of our hair, the cortex. The cortex is made up of a protein called keratin and it is the most important part of our hair – it determines the strength, elasticity, colour, and texture of our hair.

The cortex is kind of a big deal.

Inside of the cortex is the medulla which, to be honest, doesn’t really do anything. Some people, like me with blonde hair, don’t even have one.


Anatomy of the hair shaft. Source.

Journey to the centre of your cortex

The hydrogen bonds we were talking about before are contained within our hairs keratin, which now we know are in our cortex.

So, in order to change the shape of your hair, you have to be able to get past your cuticle, into the cortex. This is where a lot of damage can occur.

Your cuticle is responsible for how healthy our hair looks. The scales on our cuticle start to rise up when they are less conditioned, or are exposed to wind or heat. This can make our hair appear dry, or frizzy.

When we condition our hair, it smooths down the scales so they are parallel to the hair shaft, and makes the hair appear shiny, and healthy. The cuticle in this condition, is also doing a much better job at protecting the cortex.

If you’ve ever found your hair is difficult to curl, or colour, you probably have a very in-tact and smooth cuticle layer which inhibits heat or, colour pigment from getting into your cortex.

This is why hairdressers recommend styling your hair on your ‘second day,’ because your cuticle is a little less conditioned, and therefore less effective at protecting the hydrogen bonds in your cortex from breaking.


How can I protect my hair?

Protecting your hair consists of 3 parts:

  1. Using the right temperature for your hair type
  2. Using a heat protectant
  3. Conditioning your hair after heat styling.

Straighteners have different heat-settings for a reason. Not all hair types can withstand the same temperatures! I personally have fine hair, so my cuticle is not as thick or protective. This means I will always use the lowest heat setting on my heat tools, which is usually around 140-160 degrees Celsius. If I do style my hair, I make sure I use a deep conditioning treatment on my hair the next day, as this helps smooth down the scales in the cuticle layer, helping them seal in moisture and prevent further damage.

Scales on the cuticle layers of our hair can be smooth, or raised. When they are raised, our hair is more vulnerable to heat damage, wind damage and breakage as the scales can catch on eachother. Source: Flickr


If you have thicker hair (not density, the actually hair strand) you can use higher temperatures, but try to keep it under 200 degrees. Above this temperature, heat protectants become less effective.

Heat protectants are very important because they absorb some of the heat damage from your cuticle. This will keep your hair looking shiny and healthy. Additionally, by protecting your cuticle, you also prevent damage to your cortex which will help protect against breakage.

Another way to protect you hair is to limit heat styling. Since learning that water and heat have the same effect on our hair (breaking the hydrogen bonds), I now tend to style my hair – or more so avoid awkward kinks – by allowing my hair to dry in either plaits, a buns or brushed straight back.

It definitely saves time (and my arms – curling hair hurts).


One Response to “How does hair straightening actually work?”

  1. Felix says:

    Wow! I never new hair was so interesting!