How To Prevent Heat Damage: Set Your Flat Iron To THIS Temperature

​Want to straighten your hair but scared you won't see your curls again after you flat iron?

​Heat damage and curls that won't revert are the stuff of nightmares when you love your naturally curly hair.

​But scientists have figured out the exact temperature setting to straighten curly hair and get curl reversion every time. 

​Lack of curl reversion = heat damage

How things change. Once upon a time, curl reversion was the enemy. The quicker your curls came back after straightening with irons or a blowdryer the more of a nuisance they were.

Having hair that didn't revert all the way back after a press or blowout was a good thing. It meant you had successfully 'heat trained' your hair or, even better, you had that 'good hair' that didn't nap back up like the less fortunate.
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Fast-forward and, thankfully, people are way more educated about their hair. These days, pretty much everyone knows what a lack of curl reversion after straightening is: heat damage.

Telltale signs of heat damage on curly hair: looser curls and thinned out ends. Image by Tubarones Photography.

 
​And, after decades of work from the pioneers of the natural hair movement to undo centuries of miseducation on African hair, natural hair is mainstream.

Nowadays, it's common for people with naturally curly hair to wear their curls most of the time, even if they dabble in the occasional blowout or silk press.

Pressed or blown out hair has gone from being the main styling option for people who chose not to relax their hair to something some naturals do once or twice a year, as a length check or  temporary change of style.
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When curly is your default style, "heat-trained" hair with its limp, lifeless curls is no longer an option.  Instead, a new ritual has installed itself. 

Once the straight look has run its course, it's time to jump in the shower, douse your hair with water and wait anxiously for that moment of truth:
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"​Will my curls come back?"

​Even a couple of strands that won't curl back up can cause alarm. Fervent naturals have been known to break out the scissors immediately if their curls don't pop. Tanisha is one of them.

The last time she overdid it with the flat iron, she realized a deep trim had to happen. "From the way it flopped back on my forehead after the first rinse, I knew it. Once it was dry, I started counting all the crazy half-straight strands. I just went in and cut out the damage."

After chopping four inches off her fine afro-textured hair, which reaches the middle of her back when straightened, Tanisha says she thinks it was worth it. "Definitely.  I spend all this time and money to have healthy hair. I didn't want the heat damage spreading up through my hair."​

Curl reversion is important to naturals who try to avoid heat damage. Image by Rodolfo Quiros.

​A stress-free way to avoid heat damage

But what if it didn't have to be so stressful? What if you could tell in advance exactly what temperature you could flat iron at, get sleek, straight hair and still be sure your curls would be there after?

Temperature tips for hair straightening are all over the Internet, from professional stylists and bloggers alike. Unfortunately, very little is based on science per se. A lot of the recommended temperatures are very different too, which only adds to the confusion.
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But if you've been growing your hair heat-free for the past couple of years and want to straighten your curls without heat damage, we've got some good news for you.

Can you really heat straighten without damage?

Yes. Scientists have found out exactly what temperature you can safely flat iron your hair at without losing curls.

And guess what? One of those studies focused specifically on tightly curled hair types, which tend to get very little light in the hair science literature - though that is changing.
Working with these hair types allowed researchers to see if the protective benefits of a low temperature setting, observed in another study on looser curly hair, also applied to tightly-coiled hair.

Oh, and in another sign of changing times, this study actually namechecks the natural hair movement, crediting it as the reason women now expect to get their curls back after heat styling.

How they found out the perfect temperature

In this study, researchers looked at the effects of two heat settings: 185 degrees Celsius (365° Fahrenheit) and 220 degrees Celsius (428° Fahrenheit).

Before straightening, they classified the tightly curled hair types, using the L’Oréal hair typing system.
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The hair samples chosen were Types V, VI and VII, which roughly correspond to types 3c, 4a and 4b in the Andre Hair System.

Hair types in the curl reversion heat test. Anticlockwise from top: Type V, Type VI and Type VII by Tubarones Photography.

​To get an idea of how repeated  heat straightening would affect the hair, the team ran straightening irons on each sample at both temperatures 50 times to reflect long-term exposure at each heat level.

Then, they rewet the hair, let it air-dry  and waited to see what would happen.

Results: What temperature is safe to straighten your hair?

​When they checked the hair over at the end, this is what they found:

• 37.5% of individual hairs ironed at 220°C were unable to revert to their natural curl pattern.
• Overall, only 25% of hair bundle samples exposed to that temperature were damage-free.
• The total number of supercurly Type VI and VII strands fell after straightening at 220°C. At that temperature, there were more type V strands which were the loosest curls in the original sample.
• ​After  220 degree heat, there were even some type III and IV - wavy and loosely curled hair types like the picture below - that were definitely not present before using the straighteners.

Heat damage turned some tightly curled hair into loose curls and waves. Image by Tubarones Photography.

​But when the hair straighteners were used at 185°C, there was no overall change in curl once the tresses were re-wet and airdried. The hair straightened at this lower temperature had curls that reverted completely - even after 50 passes of the flat iron.

So does curl reversion mean no heat damage?

That strong curl reversion is a good sign for anyone who likes to rock straight hair every once in a while, but wants their curls back once the straight look is done.

On the looks of the hair alone, it seemed like heat damage didn't happen at 185°C. But that wasn't enough evidence. Heat damage isn't always visible to the naked eye, and that's why curl reversion doesn't necessarily mean zero heat damage.

So what happened when the hair was tested with advanced scientific equipment designed to detect hair damage? It's all in Part 2, which you can read right here at DHA's DIY.