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Curly Nikki

Is Low Heat Styling Less Damaging?

By January 27th, 2021No Comments

Low Heat Styling: Gentle or Damaging?

Heat styling has long been an accessible method to achieve a new hair style, whether it’s a carefully curled look or a glossy straight one.

Unfortunately, subjecting hair to the high temperatures of blow drying, curling, or flat ironing can have disastrous effects on its health and beauty. This is especially true for delicate, curly hair with its tendency to be particularly vulnerable to structural damage and breakage.

For this reason, many naturally curly haired people avoid using heat on their hair at all and rely upon air drying, scrunching or pineappling, and strategic placement of clips to impart body and shape to their tresses. However, the occasional yearning for a temporarily smooth, flat hairdo is felt by many, and the allure of the flat iron is ever present.

Low Heat Styling Tools

Many styling tools offer options to operate the equipment at lower temperatures. Recently, one company (CoolWay™, The Low heat Revolution) has been marketing a low heat flat iron styling system as a way to safely achieve straight tresses without all the damage. Among other things, their appealing claims boast that their system reduces drying time, increases hair strength by 300%, reduces breakage by 75%, and reduces frizz by 50%.

But are lower temperatures truly safer for your hair, and if so, what is the temperature threshold for safe usage? Answers to that question can be found in a deeper understanding of how thermal damage occurs, the role water plays, and finally the mechanism and efficacy of thermal protection serums in its prevention.

What does heat do to hair?

Breaks hydrogen bonds

Application of heat to the hair breaks hydrogen bonds, and the use of tension or pressure allows hair to be re-shaped so that the new hydrogen bonds form to support the new shape (straight or curled). These bonds generally remain in place until the hair is washed again or until they slowly revert to their preferred conformation, which means hair straightened via flat ironing can be silky and straight for a few days at a time.

Unfortunately, the temperatures required to achieve this effect can cause permanent structural damage to hair, especially when coupled with the relatively high mechanical forces used to change the shape of the hair. Flat irons are the ultimate players in the heat styling field, with temperatures easily reaching 350°F and even approaching (or surpassing) 400°F.

Structural defects

Hair exposed to the extreme conditions of flat irons has been observed via optical microscopy and scanning electron microscopy and both radial (outward from the shaft) and axial (along the length of the strand) cracking have been observed on hair strands, as well as fusion of cuticle scales. These structural defects become weaknesses that can result in frizz, tangling, and ultimately breakage. Loss of curl pattern is also a common effect of repeat exposure to this method of straightening.

Bubble hair

Perhaps even more disconcerting has been the presentation of what has been labeled “bubble hair” in the industry, where hair exposed to the high temperatures of flat iron straightening develops voids and bubbles along its length. Hair is naturally filled with miniscule voids that hold air, which can also absorb and retain water.

When the local temperature of this water exceeds its boiling point, which can happen very easily with exposure to high temperatures in heat styling and blow drying, it can vaporize quickly and boil out of the hair, expanding the voids to form large, vacant bubbles in the structure of the hair. These bubbles give the hair strand an irregular, knobby shape, which is not only unattractive, but also creates stress concentration sites and multiple sources subsequent of breakage.

For this reason, it is extremely important to never flat iron hair that is not absolutely dry. Any residual dampness from washing puts the hair at greater danger for extreme, irreversible damage from rapid boiling of the water molecules. Since hair is never 100% free of water (which would be an undesirable state anyway), this risk is never completely eliminated.

Minimizing Damage

Lower temperatures

Multiple variables determine the type and extent of damage done by high temperature exposure, including the condition of the hair, the temperature being applied, and the duration of the exposure. Hair in excellent condition will be more resilient and less likely to incur damage.
Outcomes are also greatly improved when lower temperatures are used and exposure times are minimized. However, evidence has been found that temperatures as low as 125°C (254°F) on a flat iron can induce formation of bubbles in the hair shaft.

The makers of Cool Way claim that the flat iron has a special sensor technology that enables it to automatically detect the moisture levels in the hair and to adjust the temperature for styling accordingly, with the additional promise that the temperature will never exceed 299°F.

This definitely is an advantage for this system over others that rely upon higher temperatures, but it is unclear whether it is sufficient to actually prevent damage to the hair. One of their claims, though, is that hair melts at 320°F, which is definitely untrue and should make the user cautiously skeptical regarding other claims made as well.

Thermal Protection Serums and Sprays

One popular method for reducing thermal damage incurred to hair when using heated styling tools is to apply specially formulated topical treatments designed to act as barriers against high temperatures. Data has shown that these products can significantly reduce the damage done to hair by flat irons and curling iron and that they also improve water retention in the cortex of the hair.

Examination of the ingredient lists of these serums and sprays reveals that the most common active components of these products are silicones. Silicones provide a variety of benefits as thermal protection materials. Cyclopentasiloxane and cyclomethicone are used to aid in faster drying time, as they are volatile, small molecule silicones. They provide protection to the hair by driving off water more quickly and minimizing the likelihood of water boiling out of the hair shaft.

Higher molecular weight silicones such as phenyl trimethicone, dimethicone, and amine-functional silicones have very low thermal conductivity, which allows them to act as excellent insulators for hair against heat. They spread easily onto the surface of the hair and form films that encapsulate the hair and not only protect against heat very effectively, but also act to seal in moisture. By preventing water molecules from exiting the hair shaft, they effectively prevent formation of voids and bubble defects. While silicones are very good in this capacity, many people prefer to avoid them or use them only minimally.

Thermal protection serums do improve the outcome of using a flat iron, curling iron, or blow dryer set on high temperatures. However, they are usually extremely high in silicones or other non-water soluble polymers, and may cause problems with buildup or lead to limp tresses for some. They definitely could not be removed from the hair purely with a conditioner or mild shampoo. So it is important to make certain that you cleanse your hair to remove these types of products once you are ready for your hair to revert to its natural state.


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!

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