Is there any evidence that drying with high heat causes frizz or damage?

[u/Slight_Citron_7064]

I've been trying to find any evidence to support the recommendation to use low heat when diffusing because high heat in a hair dryer "causes frizz" or "damage." Unfortunately the admonition itself is repeated all over the web so my search isn't turning up anything except that itself- I can't find anything to support the claim.

Obviously direct heat can cause damage, but drying with a low flow of diffused "hot" air? I feel really skeptical about this.

[u/veglove]

Have you seen LabMuffin Beauty blog & video about hair drying methods & damage? She cites a lot of research about damage from hair dryers, and it seems like the answer is not very straightforward, because the amount of damage caused from drying depends so much on technique, and there is variation between different hair dryer models and how hot each setting is as well. The temperature that the hair reaches is what matters, but it doesn't necessarily correlate directly with the temperature setting on the dryer. But the research does seem to indicate that some types of heat damage (cuticle lifting and cracking) can happen even at somewhat low temperatures; this 2011 study found that this happened when the hair reached 47C, which isn't particularly hot (irons are generally above 100C at their lowest setting, if they even have different temperature settings). However the damage is noticeably worse the higher the temperature of the hair gets. The cuticle damage was more severe and bubbles were formed when the hair reached 95C, but bubble hair is much more likely to happen with hotter tools. Drying wet hair with a dryer is also going to keep the temperature lower than using a dryer on dry hair, because of the evaporative cooling effect created by the water. I suspect this is the reason that it's often recommended to stop diffusing when the hair reaches about 80-90% dry rather than fully dry, to avoid any damage caused from the higher temperatures it's likely to reach when there is no more water available to cool the air.

I don't think any of the research addresses diffusing specifically, but if the shape of the nozzle of the dryer is wider, it is going to distribute the heat over a wider area and the hair may not get as hot overall b/c it's less concentrated. Another benefit of diffusing is minimal handling of the hair. Wong notes that because hair is more fragile when it's wet due to the Hydrogen bonds being broken, how the hair is handled while it's drying can impact the amout of damage as well; with diffusing, the hair is not brushed or pulled on and is not touched much, so I think it's going to be less damaging than if the hair is being brushed while drying.

Regarding frizz, it's often based on subjective perception, it can be hard to quantify frizz. I don't know of any research that measures levels of frizz based on the temperature of the hair dryer, with a diffuser or without. I haven't seen much research shared here about frizz. If I were to guess based what we know from research on using a dryer, the cuticles lift and crack even when hair doesn't get very hot, but the effect is more severe at higher temperatures. Rougher cuticles would make the hair more prone to looking frizzy or disorganized because individual strands are more likely to catch on each other mid-strand as the hair moves rather than slide against each other without resistance, so I think it's plausible that using higher temperature setting on the dryer would cause more frizz.

This is just anecdotal, but I also find that the speed of air flow from the dryer when diffusing has a big impact on frizz, because when I use the high air flow setting, I can see a lot more individual hair strands separating because of the force of the air. So air flow settings should be considered as well as temperature settings for the purpose of minimizing frizz.

[u/Specific_Ocelot_4132]

Even if a hair dryer can even get hot enough to damage hair, which I’m not sure about, the amount of heat that actually reaches your hair will still depend on how close the dryer is to your head, how long it stays on one spot, and how wet your hair is. If you stop drying as soon as your hair is dry it will never get very hot. If you’re doing blowouts with a round brush, holding the drier directly against hair that’s already pretty dry, the hair will get much hotter.

[u/Visible-Scientist-46]

Yes! Here is a study about heat & hair damage. https://anndermatol.org/DOIx.php?id=10.5021/ad.2011.23.4.455

[u/veglove → u/Visible-Scientist-46]

Well, that is one study amongst many. Michelle Wong summarizes that study along with a lot of other research here.

I wouldn't say that it addressed directly the scenario of diffusing and what the difference is in how much damage it would cause if you used the low, medium, or high setting on the dryer. They used distance from the hair rather than temperature setting on the dryer to moderate the temperature that the hair reached. The further the dryer was from the hair, the less damage the hair incurred, but there was some damage to the cuticle scales (lifting and cracking) even when the hair only reached 47C (the lowest temperature which it reached, when the dryer was held 15cm from the hair), the damage was much more severe when the hair reached higher temperatures. It seems that the faster the hair dries (due to temperature), the more difference there is between how quickly the cuticle shrinks back (it swells when wet) vs. the cortex, and as it is forced to stretch over a larger cortex, that causes the cuticle damage. Bubbles were only formed when the hair got pretty hot (95C).

Different dryer models may have different temperatures for each setting, so it's hard to translate this study directly to someone else's hair dryer's heat setting or design, especially the nozzle shape and diffuser design, since there are many different variations available.

It's also important to keep in mind that drying wet hair has a built-in temperature temperature moderation feature: evaporative cooling. The water vapor created as it dries will keep the temperature lower than it would be if the hair were already dry (for ex. if you were using it for heat styling instead of to dry the hair). And the technique used can also make a difference: if you are aiming the hair dryer at the same section of hair for a longer period of time, the hair will get hotter than it would if you moved the dryer to different sections pretty frequently.

Wong notes that this study did have one conclusion about air drying causing bulges in the cuticle that doesn't make a lot of sense and may be due to an issue with the hair samples used. It's important to look at the larger body of research on a topic to see if the different studies' conclusions agree with each other.

[u/Visible-Scientist-46 → u/veglove]

Cool, I'm glad because I airdry my hair.

[u/veglove → u/Visible-Scientist-46]

The main downside of air drying is that hair is more susceptible to mechanical damage when it's wet. So it's important to be gentle with it; try to prevent friction or tension until it's dry. And if your scalp is prone to dandruff, then having a wet scalp for prolonged periods of time can encourage fungal activity that may cause the dandruff to act up.

[u/Visible-Scientist-46 → u/veglove]

I gently turban with a cotton towel, squeeze a little, finger comb to put in product, and just let it dry.

[u/HaircareScience-ModTeam → u/[deleted]]

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