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Have you ever wondered whether heat protectant sprays were worth the effort and cost? Here’s the science behind how they protect your hair from heat styling damage!
What damage occurs when you heat style hair?
Straighteners and curling irons heat your hair to somewhere between 95 and 170 °C. When your hair heats up above 130 °C (266 °F), a few types of damage occur:
- The pigments that give your hair its colour change (e.g. bleached hair goes brassy)
- The keratin proteins that give your hair its strength and elasticity break down
- The outer surface (cuticle) of the hair cracks and frays
- Moisture evaporates from the inside of the hair (and if your hair is wet, the steam will blast through your hair’s structure, destroying it as it leaves)
Heat protectants claim to reduce this heat styling-related damage.
How do heat protecting products work?
Even though there are tons of different heat protectants on the market, only a few heat-protecting ingredients have been studied independently.
A 1998 study looked at the effects of PVP/DMAPA acrylates copolymer, quaternium 70 and hydrolyzed wheat protein on heat damage from a curling iron. They found that all three resulted in 10-20% less damage. 1% solutions of all three were used in the study, so they seem to work at low concentrations.
The three ingredients are quite different, so it’s likely that they work in a general way – the researchers suggest that the three all form thin films on the hair surface which slows down heat conduction and distributes heat more evenly. This means that the hair will heat up gently rather than suddenly, which causes less damage.
Many other ingredients can work this way to protect hair too – silicones, in particular, have low thermal conductivities, which means that when they’re coating hair fibres, they transfer heat slowly. Amino silicones like silicone quaterniums in rinse-off conditioners can protect hair during heat treatments according to manufacturer studies, and it’s likely that silicones like dimethicone in spray-on products can too (though they might not coat the hair fibres as well). Silicones also seal the hair cuticle and reduce moisture loss, which also helps protect from heat damage.
Since the mechanisms (lowering heat conduction, reducing water evaporation) by which these heat protectants work is so general, it’s likely that a lot of other ingredients will work to reduce heat damage too – they just haven’t been studied yet.
Keep in mind that heat protectants only reduce the amount of damage caused by heat styling. They can’t completely protect your hair – even the best results show about 50% heat protection at most.
Verdict on Heat Protectants
They work – in particular, ingredients like PVP/DMAPA acrylates copolymer, quaternium 70, hydrolyzed wheat protein and silicones (silicone quaterniums, dimethicone) reduce heat damage, most likely by evening out how the hair heats up. However, they can’t insulate your hair from most of the damage, so you still need to minimise your hair’s exposure to heat styling!
R McMullen & J Jachowicz, Thermal degradation of hair. II. Effect of selected polymers and surfactants (open access), J Cosmet Sci 1998, 49, 245-256
AL Gomes & SS Aguiar, Dow Corning Latin America, Silicones as Protective Agents in Thermal Treatments for Hair (open access)
YH Lim, CH Park & J Kim, Hair conditioning effect of amino silicone softeners in varied treatment conditions, Fibers and Polymers 2010, 11, 507-515