Blow drying is bad
Blow drying causes a “flash drying” effect that not only removes the surface moisture but also removes water that is bound to the hair, which is called water of hydration. The effect of this flash drying is that the cuticles become dried, rigid and brittle. When the hair flexes, the pressure causes the cuticles to crack. One study (see Reference 1) showed cracks occurring not only on the surface layer of cuticles, but actually two and three cuticle layers deep. Combing hair with this degree of cuticle cracking causes significant breakage.
Ironing is icky
Ironing hair causes two different types of damaging depending on whether the hair is ironed dry or wet. Ironing dry hair causes radial and axial cracking along the edges of the cuticles, which can lead to chipping. Ironing wet hair causes the moisture to burst out in little steam explosions. This causes a bubbling and buckling of the cuticle that appears as tiny hair blisters under magnification.
Helpful heat treatments
Blow dry damage can be prevented by using products containing glycerin and propylene glycol because these actives retard water evaporation. Products like Tresemme Heat Tamer Spray should be helpful in this regard. You can also look for an ingredient called “hydrolyzed wheat protein polysiloxane copolymer,” which also showed significant reduction in cracking. Interestingly, while we would expect various silicones to have a similar effect, this study showed that silicones alone did NOT reduce cuticle cracking.
Iron damage can be reduced by using conditioners formulated with low molecular weight conditioners that can penetrate into the hair like cetrimonium chloride. Another study (see Reference 2) showed that exposing hair to heat in the presence of such a conditioning agent actually caused an increase in tensile strength (the force required to break a hair). This is because the heat reacts with the conditioning agents and cross links some of the protein chains inside the hair. Look for products like Sunsilk Heat Defense Cream if you want this effect.
Additional Conditioners Containing Centrimonium Chloride
Kerastase Ciment ThermiqueLacio Lacio Leave-in Conditioner
Queen Helene Super Cholesterol*
Yes to Carrots Pampering Hair Conditioner
Silk Elements Mega Silk Moisturizing Treatment
Elasta QP DPR-11+ Deep Penetrating Conditioner
What products do you use to help prevent heat damage?