Heat styling and hair damage: safer habits

Blow-dryers, flat irons and curling irons are part of many people's daily routine. They give quick, neat results, but they can also leave hair dry, frizzy and full of split ends. If you style with heat often, you may wonder whether it is causing your hair to thin. This guide explains what heat does to hair and how to use heat tools with less damage.

How heat damages hair

The AAD warns that no matter your hair type, excessive heat can damage your hair ^{1 2}. It lists using a blow-dryer, hot comb or curling iron among the common habits that can damage hair ³.

Damaged hair is fragile, so it tends to break. Breakage can leave hair frizzy and unhealthy-looking, and if the damage continues, the AAD notes that people may eventually see thinning or even bald spots ³.

What a study found

A study in India compared 94 women ⁴. Women who had used a blow-dryer, a hair straightener, a hair iron or a perm in the past 6 months were compared with women of the same age who had not.

• There was no significant difference in hair breakage index or hair density between the two groups.
• But under the microscope, the women who used these styling procedures were far more likely to show changes in the hair structure (odds ratio 22).
• Sun exposure of more than 3 hours was also linked with microscopic hair changes.

In plain terms, the damage was visible under the microscope even when it was not yet obvious in simple hair tests. The authors called for specific guidance on hair styling for Indian hair ⁴. This was a small study that looked at one point in time, so it cannot show how much damage builds up over years.

Heat damage is mostly breakage, not hair loss from the root

Heat affects the hair strand you can see. It does not normally affect the follicle under the skin. So heat damage usually shows up as:

• Split ends and rough, dull texture
• Frizz that is hard to control
• Short, broken pieces of hair
• Hair that seems to stop getting longer

If you are shedding full-length hairs from the root, or have patches of thinning, heat is unlikely to be the main cause. See hair breakage vs hair loss and sudden severe hair fall.

Dermatologists' tips for heat styling

The AAD suggests these steps to style with less damage ^{2 3 1}:

Drying

• Wrap hair in a towel or t-shirt to absorb water, instead of rubbing.
• Let your hair partly air dry before styling, or air dry it fully when possible.
• Use the lowest heat setting on your blow-dryer.
• Blow-dry fewer times a week.

Flat irons and curling irons

• Use flat irons only on dry hair, never wet.
• Use a low or medium heat setting.
• Use a flat iron no more often than every other day.
• If you use a curling iron, leave it in place for only a second or two.
• Use heat tools less often overall. The AAD suggests aiming for once a week or even less.
• Use a product that protects hair from heat.

If your hair is already thinning

Hair that is thinning or falling out is fragile and easily damaged. For people with hair loss, the AAD recommends ⁵:

• Limiting curling irons, flat irons and hot combs to special occasions, such as a wedding or job interview.
• Using the lowest heat setting on the blow-dryer, and letting hair dry naturally when possible.
• Using a microfiber towel to help hair dry faster, which cuts blow-drying time.
• Skipping hot-oil treatments, which heat up fragile hair.

Combining heat with chemicals

Heat is harder on hair that has also been coloured, permed, relaxed or rebonded. Hair dyes and straighteners can already change the hair fibre and strip away lipids and protein ⁶. Adding regular high heat on top raises the risk of breakage. See hair fall after rebonding and hair dye and hair loss.

Styling in a hot, humid climate

Malaysia's humidity makes frizz common, and many people reach for a flat iron every day to keep hair smooth. Some lower-heat options:

• Choose hairstyles that work with your natural texture.
• Let hair air dry partly in a cool room before styling.
• Use conditioner after every shampoo, which reduces breakage and frizz ⁵.
• Avoid tight ponytails and buns to hold hair flat, as pulling adds to breakage. See traction alopecia.

When to see a doctor

See a dermatologist if your hair keeps breaking even after you change your routine, or if you notice thinning, patches of hair loss or a sore, flaky scalp ³. Your hair care may not be the root cause.

The bottom line

Heat styling can damage the hair strand, even before the damage is easy to see. A study of Indian women found more microscopic hair changes in those who used heat and styling procedures. Using lower heat, styling less often, drying gently and protecting your hair can limit the damage. Heat mainly causes breakage rather than loss from the root, so see a doctor if you are losing hair from the scalp.

Frequently asked questions

Does heat styling cause hair loss?

Heat mainly damages the hair strand, causing breakage. Over time, damage may lead to thinning ³.

What temperature is safest for a flat iron?

The AAD advises a low or medium setting, on dry hair, no more often than every other day ².

Is blow-drying bad for hair?

It can contribute to damage. Use the lowest setting and let hair air dry when possible ³.

Can heat damage be seen early?

A study found microscopic hair changes in women who used styling procedures, even when simple hair tests showed no difference ⁴.

Educational content. Not medical advice.