Temperatures encountered during blow-drying, flat-iron straightening, and hot curling processes can be high enough to cause severe trauma to the hair. Results of this can include cracks in the cuticle layer, bubbles or voids in the cortex, frayed and split ends, chipped and ragged cuticles, faded color, diminished curl and increased frizz, as well as, in Tori's case, broken strands. If avoiding high heat styling methods is not an option, it is important to take precautions to prevent or minimize damage. There are a number of products on the market advertised as heat protectant sprays, lotions, and serums which claim to prevent or repair the detrimental effects of high temperatures on hair. Are these products effective, and if so, how do they work, and which ingredients are responsible for their performance?
Heat & Hair
Flat-irons, curling, irons, and blow driers all impose extreme thermal stresses upon hair strands. With temperatures exceeding the boiling point of water (100°C) and reaching as high as 200°C or more, damage can occur by several different mechanisms.
One heat-induced phenomenon responsible for damage to hair is loss of moisture. Water molecules inside the cortex, both free and bound to keratin proteins, provide critical support to the structure and properties of hair. Evaporation of these molecules due to application of heat can alter the internal protein structure and change the intermolecular interactions that govern the mechanical properties of individual hair strands. This can change curl patterns, cause frizz, and result in hair that is less bouncy and more prone to breakage. The tactile feels of the hair is less pleasant too, having a straw-like texture. This sort of damage is pretty common with routine blow-drying.
Rapid Water Loss
The extremely high temperatures encountered in flat-iron straightening or even straightening using a hair dryer and round brush create intense conditions that can cause water to rapidly boil or “flash” off from sites where it resides within the interior of the hair shaft. This rapid boiling can create voids in the hair structure that can be seen via microscopy and look like strings of bubbles within the strand. These can cause ruptures that burst through the cuticle, leaving gaping spots in the hair, which inevitably lead to split ends and breakage. Cracks can form in the cuticle as well, making the hair vulnerable to further moisture loss and breakage. This type of damage is both severe and completely irreparable.
Hair strands are complex biomaterials that derive the bulk of their properties from the keratin protein structures in the cuticle and cortex. Thermal degradation from styling tools can occur via softening of the keratin, disruption of the three-dimensional structures due to water loss, and conformational changes in the protein. All of these changes can adversely affect the strength, elasticity, curl, shine, and texture of the hair.
Oxidation of pigment particles
High temperatures can also cause oxidation of pigments found in hair, both naturally occurring ones and artificial hair color. This fading is particularly pronounced in reds, auburns and lighter brunette shades.
Products that Protect
Heat protectants are products marketed with the claim that they prevent damage to hair from high temperature styling. Multiple studies have shown that these can be very effective in reducing, but not eliminating thermal trauma to hair. How do they work? The key ingredients in heat protectant products work in a few different ways.
Reduction of moisture loss
Since it is clearly very harmful for hair to lose its precious water molecules, one of the key tasks of a heat protectant is to both maximize and seal in moisture. Humectants such as panthenol, propylene glycol, and phytantriol are used to bind as much water as possible to the hair. Polymers, silicones, and some botanical oils are used to seal the water inside the cortex. They achieve this by coating and encapsulating the strand of hair in a film through which water cannot diffuse. Testing of both control samples and silicone-treated hair strands via thermogravimetric analysis (TGA) showed that silicone treatment significantly improved moisture retention.
Insulation from high temperatures
Silicones (especially amine-functional ones, such as amodimethicone,) some polyquats, and copolymers of acrylates are particularly effective at minimizing the damaging effects of heat styling due to their low thermal conductivity. When evenly distributed across the hair surface into a protective film, these materials act as insulators by reducing the transfer of heat from the styling tool to the hair strand. Data from thermal analysis (DSC- differential scanning calorimetry) confirmed that heat flow was reduced to hair samples treated with these types of materials.
Raw materials suppliers such as Dow Corning, Croda, and GE have also used scanning electron microscopy (SEM) and mechanical testing to evaluate the levels of protection from damage provided by various silicones and heat protectant polymers, and they found that crack formation, cuticle damage, void formation, and loss of strength and elasticity were all reduced when hair was treated with a heat protectant polymer.
What Can We Learn
If you enjoy the results of occasionally flat-iron straightening or blow drying your hair, heat protectant products can make a real difference in how your hair handles those extreme conditions. However, it is important to note that while thermal protection products containing the right mix of humectants and insulating materials can help reduce damage, they cannot completely prevent it. This means that if heat styling is frequently used, cumulative damage will occur. The only way to fix that type of damage is to cut off all the affected length. So, if you prefer to wear your hair long, use heat rarely. Another thing to keep in mind is that some of the polymers and silicones used by these products to encapsulate the hair strand may be difficult to remove and have been known to cause hair to feel sticky or tacky with repeat use.
The BeautyBrains on the best ingredients for your heat protectant--
"Which ingredients really work?
There are dozens (hundreds? thousands?) of products that claim to protect hairfrom heat damage. Do they really work? The scientific literature shows only a few chemical compounds that have been studied and shown to provide a real, measurable benefit. For best results, look for leave-in treatment products that have these ingredients in listed toward the top of the ingredient list (in the first 5 ingredients, or so):
-PVP/DMAPA acrylates copolymer
-Hydrolyzed wheat protein
Audrey Sivasothy on selecting the right heat protectant--
"A heat protectant should always be used whenever a heated appliance comes near your hair. Not only do they protect against heat damage, but they reduce hair friction ensuring a smooth glide through the plates. What you want is something that will absorb most of the direct heat from your device, yet still conduct enough heat to temporarily transform your hair’s keratin. Silicone based produces like Biosilk fusion, Redken Smooth Down Heat Glide, and Chi Silk Therapy, are great for protecting the hair against heat damage. Silicones have low “thermal conductivity” which is the measure of how fast heat is able to pass through them, according to experts at Dow Corning. “The higher the thermal conductivity, the faster a material will transmit heat” they add. Water and mineral oil have higher thermal conductivities and will allow heat to pass through hair pretty quickly. Low thermal conductivity is needed on the hair’s outer surface, but water’s high heat capacity is needed internally to complement this process and protect the hair fiber. Silicones and water work together to protect against heat damage by slowing the rate of overall heating in the hair fiber. Heating the hair at a slow, uniform temperature is much easier on the hair. Dimethicone is slated to be the lowest conducting silicone (best), followed closely by Cyclomethicone- so look out for these two “cones” in your heat protectant."