Heat is one of the most common and most underestimated causes of hair damage. It affects everyone who styles regularly, whether your hair is coloured or not. It can cause breakage, dullness, split ends and loss of the kind of natural body and shine that makes hair look genuinely healthy. If you want to protect hair from heat, it starts with understanding what's actually happening every time you pick up a styling tool. 

We know how much heat affects hair, so we decided to prove it. Our Instagram reel comparing two straighteners at different temperatures reached 13.5 million views. The reaction said it all. Here's what's really happening every time heat meets hair.

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What heat actually does to your hair

When you apply heat to hair, it triggers two types of damage that compound over time.

The first is structural. High temperatures alter the keratin proteins that give your hair its strength, elasticity and shape. When those proteins are repeatedly stressed by heat, the hair shaft weakens. The result is dryness, increased breakage, split ends that travel up the hair over time and a loss of the natural bounce and shine that healthy hair has. This affects everyone who uses heat tools regularly, regardless of whether their hair is coloured or chemically treated.

The second is surface damage. Heat forces the hair cuticle, the protective outer layer, to open. A healthy cuticle lies flat and smooth, which is what gives hair its shine and its ability to retain moisture. When the cuticle is repeatedly lifted by heat and never fully recovers, hair becomes porous, frizzy and harder to manage. It also loses colour far more quickly if you do colour your hair, because open cuticles can't hold pigment.

We cover this in more detail in our guide to caring for damaged hair. The key point here is simple, the higher the temperature of your styling tools, the more aggressively both types of damage occur. Choosing the best straighteners and dryers isn't a luxury. It's one of the most practical decisions you can make for your hair's long-term health. 

The science behind 185°C

A study published in the Journal of Cosmetology and Trichology found that hair straightened at 185°C retained its structural integrity, while hair treated at 220°C showed irreversible cortex damage and increased breakage. 

At 185°C, hair enters what scientists call the glass transition phase, hair becomes pliable enough to hold a style, then sets as it cools, without causing structural damage to the cortex or the cuticle.

GHD's research and development team in Cambridge independently arrived at the same conclusion. Style above 185°C and you risk irreversible damage to the hair's inner structure. Style below it and the result won't hold, which leads to more passes with the tool and more cumulative heat exposure overall.

185°C is not a marketing number. It is the result of serious material science research, and it is the foundation that the best straighteners on the market are designed around. This is why in the salon we work with heat styling tools at the optimal temperature of 185°C.

Why this matters for coloured hair specifically

Colour-treated hair is more porous than natural hair. The colouring process opens the cuticle to deposit pigment, and even with excellent aftercare, that porosity increases over time. A more porous cuticle opens more easily under heat, which means colour molecules escape faster and vibrancy fades sooner than it should.

If you've ever wondered why your colour looks beautiful leaving the salon but loses its depth within a few weeks, your styling tools are likely part of the answer. Read more about why colour fades and how to slow it down in our hair colour fading article.

Knowing how to protect hair from heat is especially important once you've invested in colour, but the structural benefits of lower, consistent heat apply to every hair type. 

Why most tools are working against you

Many straighteners on the market heat to between 200°C and 230°C. Some go higher. The damage this causes is cumulative and often invisible until it's significant. Hair becomes progressively drier, more prone to breakage, harder to style well and lacking the shine and body it once had.

Our Instagram reel demonstrated this clearly. We left two different straighteners on coloured hair for ten seconds each. The difference in colour loss and structural damage was stark and visible. The GHD straightener, running at a consistent 185°C, caused none of the damage visible on the hair treated with the higher-temperature tool. 

This is why we're specific about what we recommend to clients and why the tools you use every day matter far more than most people realise.

Why we recommend GHD

In the salon, we use GHD tools because of the science, not just brand loyalty.

The GHD Platinum+ straightener uses ultra-zone predictive technology that monitors heat 250 times per second, adjusting across the plates to hold a consistent 185°C regardless of your hair thickness or styling speed. A GHD straightener that maintains that consistency throughout every stroke is doing something most tools on the market simply don't. The difference shows up not just in one session, but in the condition of your hair over months and years. 

The GHD hair dryer applies the same principle to blow-drying: controlled, consistent heat that dries efficiently without unnecessary thermal stress on the hair shaft. For those who curl, the GHD Curve tong range delivers defined results at the same carefully controlled temperature. 

Investing in a quality GHD hair dryer and straightener is one of the most effective ways to protect hair from heat damage over time, and to keep it looking healthy between salon visits.

If you're styling regularly, these are the tools that let you do that without the slow, cumulative cost to your hair's health. They are our recommendation for the best straighteners and dryers for anyone who wants to style without compromise. 

Heat protectant is not optional

We put this to the test on another experiment, see the results in our Instagram reel. We applied IN's Good Hair Guardian Thermal Primer to one half of a piece of bread, left the other half bare and put both in a hot oven. The unprotected side burned. The side with the primer barely changed.

It's a simple demonstration, but it shows exactly what heat protectant does. It creates a barrier between the tool and the hair shaft. Without it, even the best GHD straightener is working harder than it needs to, and your hair is absorbing more of that heat directly.

The IN Good Hair Guardian Thermal Primer is our recommendation for most hair types. It protects against heat up to 400°C, detangles, reduces frizz and adds shine with a weightless feel that won't leave hair heavy or greasy. Apply it to damp hair before you begin, comb through from root to ends and don't skip the tips, which are the oldest and most vulnerable part of the hair shaft.

The key is using something, every single time you style, to protect hair from heat.

The right brush makes a difference too

If you're blow-drying at home, the brush you use affects how much tension and heat your hair is exposed to during the process. The Fromm Elite Thermal Brushes are designed to work with heat rather than trap it, giving you a smoother, more controlled blowout without extra passes or unnecessary stress on the hair.

Watch your water temperature

Styling tools get most of the attention when it comes to heat damage, but the temperature of the water you wash your hair in matters too. Hot water opens the hair cuticle in the same way heat tools do, stripping moisture and making it harder for hair to retain shine and condition. 

Washing with lukewarm water and finishing with a cool rinse helps the cuticle lie flat, sealing in moisture and leaving hair looking smoother and healthier over time. It's a small habit that adds up.

Protecting your hair from heat is a long-term habit

Healthy hair is maintained through consistent, small decisions. It’s the tools you choose, the protectant you apply, the temperature of your water, the way you dry and style. None of these things on their own are dramatic. Together, they make a significant difference to how your hair looks, feels and behaves over time, whether you colour regularly, get a trim every six to eight weeks or anything in between.

Good tools, good prep, good protection, it’s a combination that keeps breakage down, split ends at bay and the kind of shine and body that makes hair look genuinely well cared for.

If you'd like personalised advice on the best routine and tools for your hair type, we're happy to help. Book a free consultation and we'll build a home care approach around your hair, your lifestyle and your goals.