Since the dawn of hair straighteners, we’ve always been told that heat is bad for our hair.

That on our days off, just like off-duty Victoria’s Secret models, we should let our hair dry naturally to keep it healthy and TV commercial shiny.

I’m not a model (if I was, my off-duty look would be stained grey trackies), but I do use my hair straightener everyday. Hence, on my days off, I sit on the couch for hours watching TV and let my naturally frizzy, cowlicky hair air dry.

That is, I did, until last week when I spoke to ghd’s Chief Technology Officer Dr Tim Moore, who said something in passing that legitimately blew my mind.

He said I should… stop… air drying my hair… immediately.

Heat styling hair isn't a new concept, and neither are the concerns many of us have about 'over styling' our hair or suffering heat damage from straightening everyday.

But as Dr Moore explained at the launch of ghd’s latest product, the world’s first SMART hair straightener, the reasons why drying your hair with the hairdryer on 'high' is better than letting it dry naturally is better for it makes a lot of sense.

"When hair is wet, hair becomes very weak. It loses its strength, it becomes half as long as when it's dry. If you've got wet hair and you pull a brush through it, you're twice as likely to cause damage and breakage to the hair fibres. So you don't want to leave your hair in a weakness state for any length of time," he told Mamamia.

"Secondly, when hair is wet, it swells like a sponge. Around the outside of each strand of hair, you have the cuticles, which are calcified cells than sit around like roof tiles. As hair absorbs water and starts swelling, it puts pressure on those cuticles and they start to break and come off, causing damage. That's why it's not a good idea to leave hair fibres in damp, wet conditions for any extended period of time."

Put simply: Everything those off-duty models told us about letting our hair dry naturally on our days off was a lie.

Yes, Dr Moore said we can still damage our hair through heat styling, but not if you do it the right way.

"People think a hairdryer will cause damage, if you do it in the right way, it won't. When you start drying the hair, it heats up to around 30 degrees, then holds that heat for two minutes depending on how thick your hair is," he explained.

"The reason for that is, if you think of it like when you get hot and sweat, sweat cools you down by evaporation. It's the same thing happening here, the water on the surface of the hair fibres evaporating keeps the hair fibres themselves cool. Only once the water has evaporated off, you'll see the hair increase in temperature again. If you're using your hair dryer on a low setting, you'll be fine."

Side note - speaking of hair damage, here's the struggles only bottle blondes will understand. Post continues after video.

Dr Moore's recommendation for drying your hair to prevent damage is to start on a low setting - "you'll have to be patient" - and then turn the hair dryer up to high once you can feel the majority of the surface water has come off. Also avoid directing the heat onto any one area for too long.

If you're short on time, he also said "using a hair dryer on a high setting if you have to get it dry quickly is better for your hair than letting it dry naturally."

Yep.

As for the concept of heat damage, Dr Moore explained it's got everything to do with the 'magic numbers' at which the bonds in your hair break at.

"Anything above 200 degrees and you start to cause significant damage to the hair. The damage starts building from anything higher than 185 degrees, as those temperatures starting breaking the disulphide bonds, leading to major hair damage," he said.

"There are, however, bonds in your hair you actually want to break. The bonds you need to break to put a style into the hair are called hydrogen bonds. Hydrogen bonds are more like magnets; you can click them together and break them apart as many times as you won't and you won't get any damage [locking the style into place]. Those bonds start to break at 147 degrees for all types of human hair."

Bringing it back to drying your hair with a hair dryer, the average temperature of a low setting is between 70-80 degrees, and a maximum of 120 degrees on high. Even though your hair is weaker when it's wet, and therefore the bonds within can be broken at a lower temperature, your hair dryer will only reach a temperature high enough to break the hydrogen bonds, like when you get a blow dry in-salon.

I know. It's a lot to take in.

But if only one piece of information sticks in your brain today, make it this: If in doubt, reach for your hairdryer.

How often do you use heat styling tools to style your hair? Do you worry about heat damage?