I’ve been straightening and also curling mine hair wet/damp for years, despite all the popcorn-sounding fizzes and also crackles – but some science I’ve newly read have actually made me carry out a complete 180. It transforms out wet and dry hair respond to excessive heat very differently – and wet hair cops it far worse, and also not just because it’s an ext fragile.

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First, a small refresher ~ above hair anatomy. Hair has actually three main parts:

the medulla – boring central core, actually non-existent in light and also fine hairthe cortex – middle layer, responsible because that colour, texture and also most of the toughness of hairthe cuticle – safety outermost layer, made of overlapping cells favor roof shingles or fish scales, shiny

The cuticle lays flat, yet water can gain in in between the gaps. When you wet healthy and balanced hair, it have the right to actually absorb as much as 30% the its own weight in water right into the within spongy cortex (more if it’s damaged hair).

An mean hair straightener heats approximately 185-230 °C. Curling irons are a tiny cooler, in ~ 95-200 °C. They’re both well over the typical boiling suggest of water, i beg your pardon is 100 °C. (Temperatures in Fahrenheit space straighteners 365-446 °F, curlers 203-392 °F and boiling water 212 °F, for any readers indigenous non-metric countries like the US, Liberia or Myanmar.)

C’mon USA, switch already. I believe in you.

What happens as soon as the wet inside of hair gets heated well beyond its cook point? Well, it’s not as well dissimilar to popping corn…


When water transforms from liquid to gas that expands. As soon as it’s heated strongly it expands rapidly. Since it’s border in the cortex by the cuticle, it needs to bust out. That’s right – the water explosively evaporates, wrecking whatever’s in the path, which wake up to be… her hair.

From Gamez-Garcia, J Cosmet Sci 2001, 62, 109-120

(Hair go not commonly look this spongy increase close, in instance you’re wonder – it must look choose sliced playdough with a small spongy section ideal in the middle.)

It’s not only on the inside the the cook water wreaks havoc – it’s obtained to gain out somehow, and also in the rush to leave it bangs increase the outside of your hair cuticle pretty good too – rather of lie flat, the “shingles” or scales of her cuticle are now bumpy from gift pummeled native the inside:

From Ruetsch and Kamath, J Cosmet Sci 2004, 55, 13-27

Don’t freak out too lot – this probably happens greatly to the hair that’s right versus the heating plates of her straighteners and curling irons (it’s law the rest of your hair a solid, sacrifice itself because that the greater good!). But if you’re act this to her hair every day, the damage builds up.

Of course, dry hair doesn’t obtain away unscathed – it still reasons microscopic cracks on the hair’s surface, denatures hair proteins, and decomposes pigment – yet this wake up in wet hair too. All this damage goes ~ above to give you dull brittle hair, break-up ends, brassy colour, enhanced tangling and also breakage.

What can you do? Well, obviously, you need to straighten and also curl her hair only when it’s dry! you can likewise invest in a warmth protecting spray (most of this work, to part extent!).


M. Gamez-Garcia, Void and pore formation inside the hair cortex through a denaturation and also super-contraction procedure occurring throughout hair setup with hot irons, J Cosmet Sci 2001, 62, 109-120.

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S. B. Ruetsch & Y. K. Kamath, impacts of thermal treatments with a curling iron on hair fiber, J Cosmet Sci 2004, 55, 13-27.