Heat damage is the most common cause of dry, brittle, split hair, and unlike most hair problems it does not recover. The strand is altered, and the only remedy is growing it out and cutting it off.

That is the case for taking this step seriously.

What a protectant does

It does not make hair heatproof. It forms a barrier that slows how quickly heat transfers into the strand, and helps distribute it more evenly so no single spot takes the full temperature.

That reduces damage substantially. It does not eliminate it.

Temperature matters more than the product

Most people style far hotter than they need to:

  • Fine or damaged hair — up to about 150°C
  • Normal hair — around 180°C
  • Coarse or very thick hair — up to about 200°C

Above 200°C you are into the range where damage happens quickly regardless of what you applied first. If your tool has one setting and it is very hot, that is a worse problem than which spray you use.

Using it properly

  1. On damp hair for creams and most sprays; dry hair for products specified as such — check the label, because using a damp-hair product on dry hair does very little
  2. Section the hair and apply evenly. Spraying at the outside only leaves the inner layers unprotected
  3. Let it dry before applying heat if the product says so. Heating wet hair with a straightener causes the worst damage there is
  4. Do not over-apply. Excess makes hair sticky and can itself cook onto the strand

The habits worth more than any product

  • Fewer passes. One slow pass does less damage than four quick ones
  • Lower temperature, always the first thing to try
  • Rough-dry to 80% before using a straightener or curler
  • Heat-free days. The single most effective measure available
  • A cooler dryer setting, which takes longer and does markedly less harm

Which format

  • Spray — lightest, suits fine hair and daily use
  • Cream — more substantial, for dry or coarse hair
  • Serum or oil-based — smoothing as well as protecting, best on ends
  • Combined leave-ins — convenient, and check they actually state heat protection

The honest summary

Use a protectant every single time, style cooler than feels efficient, and take days off. Those three together preserve hair; a protectant alone at 220°C does not.

For repair once damage has happened, see the hair mask guide.