The science of drying your hair

By a Cambridge academic who has dedicated his life to studying it

PhD in Microelectronics from Cambridge University and Chief Technology Officer at ghd

“My own hairline may be receding, but I can promise you I know this: a perfect blow dry is no accident. Few women know there’s a scientifically proven technique which will give you the ultimate blow dry.

Indeed, it’s my job to research how washing and styling can help, or harm, human hair – and from examining hair at the deepest cellular level, I’ve uncovered the secrets of attaining the perfect do.

For example, did you know that leaving your hair to dry naturally is actually more damaging than blow-drying it? Or that going to bed with your hair damp could be giving you split ends?

That’s just a taster of the secrets I’ve uncovered. By training I’m a physicist, with a pHD from Cambridge University and a deep interest in materials. You might not think it, but our hair is a fascinating material – it responds to many different environmental stimuli, even the weather.

So here’s my guide to the perfect way to dry your hair…


Before you can understand how to do the perfect blow dry, you need to understand some of the science behind your hair’s structure. Hair is made from the protein keratin; the same substance as nails, feathers and claws. It’s a very complicated structure; each individual shaft is like a rope within a rope. There’s a protective outer layer known as the cuticle, which is calcified keratin, making it hard like fingernails. In the middle is the cortex, which is also made from keratin, but is more flexible as it’s not calcified. The cortex gives the hair its strength and elasticity.

We each have between 100,000 to 150,000 hairs on our heads. Asian hair is the thickest and strongest, measuring between 80 and 100 microns (a millionth of a metre) and is completely circular in diameter. African hair is elliptical, or oval, and is also the thinnest - at around 50 microns. Caucasian hair falls between the two; measuring between 50 and 80 microns and is slightly elliptical. On average, we lose 50 - 100 hairs every day.

   ghd air® development process


You might imagine that leaving your hair to air dry, without the heat of a hairdryer, would be best for it. Wrong! In fact, this is possibly the most damaging thing you can do to your hair.

How? Well, it all starts the moment you wet your hair. It changes the molecular structure of the strand straight away. Because when water is applied to hair, it is absorbed through the hard outer layer of cuticle into the cortex, which then swells up. This means it’s instantly weakened. The cuticle acts like a bit like roof tiles, with water going in between the gaps.

Leaving hair to dry naturally can be more damaging than intense heat. Hair can absorb up to 30 per cent of its own weight in water. The longer it stays wet, the worse things get, as it continues to swell. This is because repeated swelling followed by slow drying of hair causes something called the cell membrane complex (essentially the glue holding the cuticle together) to crack, permanently damaging the hair. You’d be better off drying your locks quickly with heat, rather than going au natural.


We’ve looked at all sorts of different shampoos and conditioners, from basic to high end, and despite what you might hope, there was no question that price made a difference. Fascinatingly, though, it was the most luxuriously expensive bottles that weren’t worth the price-tag. Once you start paying £30 or more, the results plateau.

But very cheap products aren't much cop either.

Instead, choose a mid-tier brand who specialise in hair care. And up to the £30 a bottle mark, the more you can spend, the better the result.

Despite the promises on the side of the bottle; no product, no matter how high end, will actually strengthen your hair.

Certainly though, any post-shampoo slosh of conditioner will reduce friction between the hair by making it more slippery and therefore less likely to break.


You’re out of the shower and no doubt you instantly grab your hair dryer. But there’s one vital thing you must do first – and that’s towel-dry your hair. To do this, you should scrunch gently to remove excess water. Don’t rub! Rubbing may break weakened hair, and the resulting different lengths of strands only cause hair to look frizzy.


Don’t brush wet hair. Use a wide-spaced comb like the ghd detangling comb, but never a brush, and go slowly to minimise damage. A brush may actually tear your water-weakened locks, causing instant breakage.


You should never go to bed with damp hair. It may be tempting to save time and only half dry hair before bed, but this is a terrible mistake. You might be causing irreversible damage, which could take months to grow out. When you move your head around in your sleep, as we all do; the friction against the pillow could be enough to cause breakage. Even slightly damp hair is a bad idea.

It’s the same if you leave the house with damp hair. The cortex could continue to swell and crack, which will take years to grow out. And because the gaps within the cuticle are larger in wet hair, meaning that more can be absorbed into the cortex; strands can be badly damaged. For example, your hair can be affected by moisture and humidity in the environment, so it may rapidly become frizzy and dull – or the effects of pollution, with chemical particles causing damage and dryness, can be exacerbated.


While we’ve always been taught that drying our hair is bad, our research reveals that it’s actually better for you than risking damage by leaving it to dry naturally.

Once you’ve towel dried and combed through, dry your hair till it feels warm. Use the ghd aura® hairdryer or ghd air® hairdryer on a low heat and speed setting at first. This is so the hair doesn’t over heat (remember it’s far more vulnerable to heat when wet). You should dry in sections. Even if the hair dryer temperature feels warm – it will probably be around 70 degrees – the temperature of the hair won’t go over about 30 degrees until it dries.

Ideally, you should hold the hairdryer 15 centimetres from the head and dry with a continuous motion. Obviously this is easy for a stylist and not so simple at home, so we suggest holding the dryer as far back as you can comfortably reach, on a low air speed setting and keeping it moving slowly.

As soon as hair starts to feel warm it will be about 90 per cent dry, and you can turn up the heat.

It’s vital that you don’t forget to give it a blast of cool air at the end. It makes a massive difference, ensuring the hair’s internal bonds are remade and sealing the style in place.


Turning your head upside down does give volume, but it’s not strictly necessary. Volume is actually created by the hair strands coming out of the head at a higher angle. So the best thing is to get the nozzle of the dryer as close to the scalp as possible to get lift. Diffusers can help with curly hair, as they dry hair slowly and provide volume, lifting moisture out. The air circulates around the curls, defining them and minimising frizz.


Creating a shiny look is mostly down to simple strand alignment – i.e making sure it’s all pointing in the same direction. To do this, section your hair and dry one area at a time, aiming the dryer downwards as much as possible. This will blow out knots and tangles. Ensure the nozzle of your dryer is narrow, as it makes an enormous difference to the final results. Both the ghd aura® hairdryer and ghd air® hairdryer have concentrator nozzles which are narrow. If the nozzle is large and wide open, you aren’t going to get a defined airflow. It’s like putting your head outside the window of the car to dry it.


Only use straighteners or curling tongs on completely dry hair. Applying the heat of tongs to wet hair is catastrophic. As you heat water and turn it from liquid into gas, it expands. Water which is trapped in the cortex will burst out, causing damage. If you’re really trying to fix a style in place, use hair spray – ghd final fix hairspray - after drying and before straighteners, but allow to it evaporate before using heated gadgets. You can use it afterwards as well to further fix the style.

Invest in good quality tools. Use the ghd platinum® styler and ghd curve range all of which heat to the optimum temperature of 185 degrees consistently and evenly across the plates and barrels to give you the ultimate styling results and healthier, shinier and stronger hair - all in one stroke.


It might sound bonkers, but the weather can really affect the quality of your blow dry. It’s less about rain or shine however, and more about the moisture in the air. If it’s humid, the style will drop more quickly. Use a heat protective spray or a curl hold spray to reduce the effect of the humidity. The ideal weather to achieve a perfect blow dry is a very dry, cold, sunny day at zero degrees. Which might explain why your best hair days happen in the winter, not summer!”

Q&A with Dr Tim:

What are your top tips to style your hair without damage?

- Dry your hair with a scrunching motion - no rapid, aggressive rubbing.

- When drying your hair: start on a low temperature and speed. Work on a section by section basis and when you feel your hair increase in temperature, move on to the next section. Once complete, you are ready to style.

- When using a thermal styling product, the optimal temperature is 185 degrees celsius. Anything higher will burn and melt your hair and anything much lower will mean it is harder to style your hair to get shine and longevity. ghd styling tools maintain a consistent healthier-for-hair heat of 185 degrees celsius.

Hair has what is known as a 'Glass Transition Phase': above the glass transition phase temperature, hair acts like hot glass so you can easily shape it. Cool below this temperature and it will retain the shape it was left in. This is repeatable and can be done without damage. At high temperatures like 210 degrees celsius, the fundamental structure of hair - the di-sulphide bonds - start to break down and the hair becomes very weak. It is a bit like cement being removed from a brick wall.

What are your top five tips for looking after our hair?

1. Never brush wet hair. Use a good conditioner after washing and comb through

2. Don't leave your hair to dry naturally - hair is weak when wet

3. Using thermal styling tools is absolutely fine: but no more than 185 degrees celsius. Anything higher and you'll fry it. There is no need for variable temperature. ghd styling tools maintain a consistent healthier-for-hair heat of 185 degrees celsius

4. Eat and exercise well and destress. Hair is a by-product of what you eat. Poor diet = poor hair. Eat foods with plenty of iron in them. Walking / hiking is a good form of exercise - long lasting and gentle

5. Use a scrunching motion when towel drying

What are your favourite facts about hair?

- It is so complicated that no one yet fully understands it.

- It is phenomenally strong: you could make a bullet proof vest out of it. A whole head of hair could support 2 elephants.

How long have you worked with hair?

10 years.

How did you get in to it?

Working as a technology consultant in Cambridge you get to work on all sorts of science and technology problems - developing hair styling products which cause no damage yet create long lasting style and tons of shine was a fascinating science and technology problem - I got pulled in as a scientist and started working for ghd.

The essential drying products:


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