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    • How does heat damage hair?

      The signs of heat damaged hair are hard to miss, but what causes damaged hair? There are many factors that can contribute to hair damage. Dying and bleaching your hair uses chemicals that cause damage. Your hair can get sunburned, and brushing or combing vigorously can cause the strands to pull too far, leading to possible snapping and breakage.

      Another major culprit of damaged hair is heat.

How does heat lead to damaged hair?

Using hot tools like blow dryers, flat irons, and curling irons increase the chances that you'll experience damaged hair from heat. Some hot tools don't allow for temperature control. They may have only one setting or basic options low, medium, and high. 


Some tools have more control but have temperatures that can reach a max of more than 400°F. You'd expect that the hotter the temperature, the better the styling, but that's not the case. 

Exposure to high heat changes the shape of your hair’s keratin strands. Temperatures over 300°F convert the ⍺-keratin to β-keratin, which eventually leads to weaker hair that has lost its elasticity and become more prone to damage. When the keratin is melted, your hair maintains that shape on a molecular level, and it's not reversible.


Heat damaged hair: causes, treatments, and prevention

Damaged hair lacks moisture

One way that heat damaged hair occurs is through a loss of moisture. Your hair is made up of different bonds, including 4% fats, oils, and pigments, 17% water, and 79% keratin proteins. The cortex is the inner part of your hair strands, and it contains water molecules that are bound to the keratin proteins.

When heat is applied, the natural oils are stripped from your hair, and the water molecules evaporate, changing the hair’s protein structure. The high temperatures cause the water to dry up quickly, which affects the structure of each strand and can crack the cuticles, the outer layer of hair, making hair more vulnerable to further damage. 


Hair cuticles have shingles that overlap, like a roof. On healthy hair, these shingles lie closed and flat. When hair is damaged, the shingles open and rise up, causing split ends and tangles. The raised cuticles also allow more moisture to escape.


9 Signs of heat damaged hair

Damaged hair is highly porous

The cuticles are what protects the cortex. When the cuticles are broken, damage can reach the cortex and your hair becomes highly porous. Damage to the cortex also results in weaker hair that's less elastic and more prone to breakage.

Hair porosity is categorized as low, normal, or high. To test your hair’s porosity, drop a strand of hair in a cup of water. If the strand sinks to the bottom of the cup, you have highly porous hair. If it floats to the top, it's low, and if it stays in the middle, it's normal porosity. 


Heat damage can also cause the pigments of your hair, whether it's natural or dyed, to oxidize. The result is faded coloring, especially when hair has high porosity. If you dye your hair, this might mean that you need to apply color more often, which can cause further damage.

Understanding heat damaged hair

In a study from the Journal of Cosmetology & Trichology, researchers examined the effects of two flat iron heat settings on natural, curly hair: 365°F and 428°F. Before straightening, the hair type was categorized as tightly curled.


Hair was straightened 50 times at both temperatures. Then the hair was rewet and air dried to see how the straightening affected the curls.


The hair that was straightened at a temperature of 365°F didn't experience any overall changes in the curls. Of the hair that was straightened at 428°F, 37.5% of the participants couldn't regain the natural pattern of their curl.


Though the hair started out as tightly curled, the end result was looser, bigger curls or waves that were almost straight. Only 25% of the hair exposed to the higher temperature was damage free.


Researchers also conducted a tensile test on 50 strands of the straightened hair, which put stress on the hair to the point of breaking. The hair straightened at 365°F didn't become weaker or have more breakage than before it was straightened. The hair strands that were straightened to 428°F became weaker and less elastic, making them more susceptible to breakage. 

What does damaged hair look like?

There are many signs that you're healing with heat damaged hair.

Damaged hair looks rough, dry, dull, and frizzy. It loses its natural shine because the cuticles, which give hair its sheen, have been damaged.


Heat damaged curly hair may appear limp, and the curls may not hold their shape, and straight hair may not appear as polished and sleek.

On average, you lose about 50 to 100 hairs per day, but when your hair is damaged, you'll likely see more hair loss and flyaways from breakage.


Can heat damaged hair be reversed?

Managing heat damaged hair

Can damaged hair be repaired? Once the structure of your hair is changed by heat damage, it's permanent. There are a few options for managing the situation.


You can cut your hair and remove the damage, but this could require a big chop depending on how extensive the damage is. This could be anything from less than an inch to several inches.


If you're not ready for short hair, you can care for your tresses and take steps to manage the damage to your hair while you grow it out, cutting off the ends each time you get a haircut.


According to Elle, hair that's highly porous should be treated with leave-in conditioners, creams, and oils like argan or jojoba. This helps seal in moisture to help your hair feel softer. High porosity hair also needs more protein, so try using products that have keratin, silk, or wheat protein in the ingredients.


Keep the use of your hot tools to a minimum and aim for a temperature between 200°F to 300°F when you do blow dry, straighten, or curl your hair. Use a heat protectant and try to let your hair air dry whenever possible.


Heat damaged hair treatments



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