The Curl Chemist explores popular low heat styling tools and reveals the the truth about the damage they cause.


Although it is becoming popular to lower heat tools to change the shape of your hair, it is critical to remember that it really requires relatively low temperatures to cause irreversible damage to your hair structure.

The Coolway™ Low Heat styling system's ability to adjust temperatures automatically based upon the condition of your hair is an interesting technology, but in comparison to other very high temperature flat ironing tools the improvement is only marginal.

The temperatures used in devices with adjustable heat settings are substantially lower than the 400° often seen in the most powerful flat irons, but they are still sufficiently high to cause structural damage to the hair.

There is an important relationship between the transmission of thermal energy and the size of the object receiving the energy. Hair strands are very small, as are the proteins, lipids, and water molecules which comprise them, and energy is transmitted very rapidly into those structures.

Remember that water boils at 212°F, and individual molecules can reach that temperature very quickly and easily, even with temperatures of only 200°F on the styling tool. Keratin proteins are denatured at even lower temperatures.

The longer a tool remains in contact with the hair, the more thermal energy it conveys to each hair strand which can lead to really catastrophic damage, such as bubbles, voids, distortions of the geometry of the hair, permanent disruption of the curl pattern, fusing of cuticle scales, and ultimately, breakage.  For this reason, gliding a flat iron quickly across the surface of the hair, in one swift, smooth movement is critical.  Damage is cumulative, so frequent use of high heat styling methods increases the chances of noticeable degradation of the health of the hair.

Thermal protection sprays and serums utilize silicones and other polymers, which have been found to provide some degree of protection when used in heat styling applications.  However, these products are prone to accumulation on the surface of the hair, which can cause dryness, frizz, and limp tresses.

It seems if one wanted to occasionally sport a straight hairdo, then using a lower heat flat iron is indeed a safer choice by which to achieve that end.  However, subjecting one's hair to these conditions on a daily or even weekly basis will inevitably cause structural damage to the hair, which is just not reversible.  We take too much care with the condition of our hair to risk it too often in pursuit of those flat, glossy styles. Embrace your curls!

MORE: Low Heat Styling Tips for Curly Hair


  1. Zhou Y, et al., The effect of various cosmetic pretreatments on protecting hair from thermal damage by hot flat ironing, J Cosmet Sci. 2011 Mar-Apr;62(2):265-82.
  2. Christian PWinsey NWhatmough MCornwell PA, The effects of water on heat-styling damage, J Cosmet Sci. 2011 Jan-Feb;62(1):15-27.

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Tonya McKay

Tonya McKay Becker is a curly-haired polymer scientist and cosmetic chemist whose academic and industrial research experience have provided her with expertise in the fundamentals and applications of polymer science and colloid chemistry. She has long had a fascination with the structure-property relationships of the complex solutions used in hair and skin care products, and how they interact with and impact these remarkable biological substrates. Ever curious, Tonya has dedicated herself for more than a decade to honing her expertise on the science of curly hair, how it differs from straight hair, and how product ingredients used on curly hair affect its health and beauty. Her passion for sharing this knowledge with others has led to her current career of educating people from all backgrounds who share an interest in this exciting field.