Heat Protection for Hair — Which Ingredients Shield Against High Temperatures?

Why does hair need heat protection?

Human hair is made up mainly of keratin — a protein with a complex tertiary structure stabilised by disulphide, hydrogen and ionic bonds. Temperatures above 150 °C start to break the hydrogen bonds (responsible, among other things, for the hair's shape), and above 230 °C the disulphide bonds are permanently damaged and the keratin is denatured.

The trouble is that popular flat irons operate in the 180–230 °C range, and some models can even be set to 250 °C. Without a proper protective barrier, every use of a heat tool means micro-damage to the hair's structure.

How do heat protection products work?

Heat protection cosmetics work on two levels: see the details in our ingredient encyclopedia.

1. They form a physical barrier — a film on the hair surface that slows the transfer of heat into the cortex.
2. They bind water — some ingredients hold on to water molecules that, as they evaporate, draw heat away (a cooling effect through evaporation).

No heat protectant eliminates the effect of heat on hair by 100% — but it can significantly reduce damage, especially at temperatures up to 200 °C.

Key heat-protective ingredients

Silicones — dimethicone, cyclomethicone, amodimethicone

Silicones are the most popular heat-protective ingredients. They form a thin, hydrophobic film on the hair that:

• Slows the transfer of heat from the tool into the hair cortex
• Seals the cuticle scales, adding shine
• Reduces friction between hairs (making detangling easier)

Dimethicone forms a thicker, more durable layer — good for thick, porous hair. Cyclomethicone (cyclosilicone) is light and volatile, so it doesn't weigh down fine hair. Amodimethicone binds selectively to damaged sections of the cuticle — working exactly where it's needed most.

You can read more about silicones in our guide: Silicones in shampoos — why it pays to check them.

PVP (polyvinylpyrrolidone)

PVP is a film-forming polymer that creates a flexible, invisible coating around the hair. At room temperature it is colourless and odourless, and when exposed to heat it hardens, forming a firmer protective barrier.

• Pros: lightweight, doesn't weigh hair down, dissolves well in water (easy to wash out)
• Cons: in high humidity it can feel sticky
• Best for: fine, delicate hair

Wheat protein (hydrolyzed wheat protein)

Hydrolysed wheat proteins are short chains of amino acids that penetrate the hair cortex and strengthen its structure from within. When exposed to heat, they form additional cross-links with keratin, increasing the hair's resistance to thermal damage.

• Pros: strengthen hair structurally, not just on the surface
• Cons: too much protein can stiffen hair ("protein overload")
• Best for: damaged, porous hair

Other supporting ingredients

• Quaternium-70 — a silicone derivative providing heat protection and easy detangling
• Panthenol (provitamin B5) — binds water, improves hair elasticity
• Arginine — an amino acid that strengthens the bonds in keratin

Check which ingredients your favourite product contains — enter its name in the PurScore search.

Spray vs cream vs serum — which to choose?

Temperature thresholds — how much can hair take?

• Up to 150 °C — a safe zone for most hair (blow-dryer on a low setting)
• 150–180 °C — the onset of hydrogen-bond breaking; heat protection strongly recommended
• 180–210 °C — the standard range for flat irons; heat protection essential
• Above 220 °C — risk of permanent damage even with heat protection; avoid these temperatures

How to use heat protection correctly?

1. Apply the product to damp hair (not wet, not dry) — moisture helps it spread evenly.
2. Work it from the mid-lengths down to the ends — the roots are naturally healthier.
3. Wait until the product absorbs or dries (1–2 minutes).
4. Set the tool to the lowest effective temperature — for most hair types that's 170–185 °C.
5. Don't run the flat iron over the same section repeatedly — one smooth pass is enough.

Summary

Effective heat protection is a combination of the right ingredients (silicones, PVP, proteins), the right product form and a sensible tool temperature. There's no miracle cosmetic that will shield hair from 250 °C, but a well-chosen product can significantly reduce damage in everyday styling.