Stop drying your hair wrong: the science

what's the best way to dry your hair according to science? is it hair dryers hair straighteners towels or just leaving it to dry naturally? I'm Michelle I'm a chemistry PhD and cosmetic chemist and as someone with fragile expensively damaged hair who tries a lot of hair products I have a special interest in this here's the science of drying your hair first we need to talk about what happens when hair gets wet how hair interacts with water hair has a complicated structure with lots of different parts most of these like water especially the inside which is

called the cortex so when your hair is properly wet like when you're washing it it swells up undamaged hair can absorb up to about a third of its own weight in water damaged hair has more gaps for water to fill sort of like a more bubbly sponge so damaged hair will hold on to even more water and what water does really well is break hydrogen bonds your hair is held together by lots of bonds which give it its strength and shape some of these are pretty permanent they only really break with chemical treatments but hydrogen

bonds are temporary they break and reform all the time about a third of your hair's strength comes from these temporary hydrogen bonds when your hair is dry hydrogen bonds are sticking hair proteins to hair proteins it's sort of like they're holding hands they're essentially glued together at a molecular level but water can also form hydrogen bonds so when your hair is wet your hair proteins start bonding with the water instead of with each other these are a bit like you and your dog are at a dog park you have a strong bond he comes when

you call him Timmy (the boy was named after the dog) but adding water is like adding a whole bunch of really friendly puppies you're both having interactions with all of these new puppies you and your dog have a temporarily weaker bond but when these other water/puppies leave the hair/park you and your dog have a stronger bond again now looking at this diagram can you see the problem? the water isn't attached to anything so the two halves of this hair protein ladder have broken rungs they are less glued together I will never run out of analogies

for this less hydrogen bonds holding everything together means that your hair is weaker you can actually test this for yourself try stretching a strand of your hair when it's wet and a strand of your hair when it's dry the wet hair will be stretchier feel free to pause this video and try this out I will still be here when you come back I promise on top of this the cuticle scales in your hair those overlapping roof tile scales on the surface they don't absorb water evenly the underside of each scale absorbs more water than the

top and the glue in between the scales also absorbs water this means that the bottom expands the scales get pushed up away from the hair they stick out more and they get snagged and chipped more easily so water in itself isn't really damaging to hair you might have seen some stuff online about hydral fatigue the idea that just water will damage hair but the evidence doesn't really show that water on its own has much of an impact but when your hair is wet it is in a more fragile state so anything that you do to

your hair physically that can cause damage if you do it when it's wet that damage gets magnified there are exceptions one really big one is detangling curly hair check out my old video that explains this so what all of this means for drying wet hair: with any method that you use technique will make a massive difference rubbing your hair with a towel like you're trying to start a fire is very different from blotting and squeezing it gently you can imagine those little sticky up hedgehog spine cuticle scales bashing against each other yanking your hair violently

with a round brush while using a blow dryer is very different from gently spreading out your hair with your fingers and moving it around even with leaving your hair to air dry naturally sleeping on wet hair and smooshing it into your pillow with the full weight of your galaxy brain or having your hair jammed between your back and the couch as you watch a stressful movie that's very different from letting your hair dry in peace the other really big thing we need to talk about is heat heat can cause a lot of different types of

hair damage proteins in your hair can change shape or break down which makes your hair weaker substances inside your hair can oxidize and change color this can make your hair look yellow and if you have dyed hair the eyes can break down and change their color heat can cause microscopic cracks and cavities in your hair especially at the surface and your cuticle scales can lift this makes your hair rougher and duller but on the bright side it can make your hair less oily because the gaps can hold onto oil see there can be upsides to

damage! and we need to talk about bubble hair if your hair is wet and you heat it near the boiling point of water above about 90 °C the water inside the hair can evaporate faster than it can escape it boils explosively it basically punches its way out of your hair and leaves bubbles inside your hair is basically popcorn like and subscribe if you want the algorithm to give you more analogies that I will probably regret one day when someone takes them out of context with all of these types of damage the more heat that you

use the worse it gets and there are some changes that don't happen until you get to a particular temperature usually you get a ton of damage from about 180 ° yes that is Celsius I do not rock with Fahrenheit so using a standard hair straightener on wet hair is one of the most damaging ways to dry your hair if you're hearing snapping and crackling that is water boiling quickly and some of that might be the water inside your hair turning it into rice bubbles blow dryers aren't anywhere near as hot so the level of damage

is very different you probably don't need to use heat protectants either when your hair is still wet the water evaporating helps cool down your hair so it doesn't usually heat up too much plus all that air also helps your hair dry it's best to move the dryer around to try to dry your hair evenly so you're not like heating up already dry strands for no good reason the distance between the dryer and your hair also makes a really big difference like in this study the researchers washed and dried hair samples every day for 30 days

with different drying methods there's just leaving it to air dry and then using a hair dryer at different distances the further away the hair dryer the lower the temperature and the longer it took to dry they found that all of the samples that were dried with a hair dryer had damage to the surface of the cuticle with higher heat causing more damage the cuticle scales lifted and cracked there were also signs of bubble hair at a distance of 5 cm which is about this much this translated to a hair temperature of 95 °C and this

agrees with other studies the cracking is thought to be because hair makes the outside cuticle dry faster than the inside cortex so the outside is shrinking faster than the inside the inside kind of Hulks out and cracks the cuticle around it and there have been reports of bubble hair with hair dryers but they're usually when the hair dryers are used really close so hair gets really hot most of the time it is the hotter curling irons and straighteners that have the risk of like properly swiss cheese hair with really big holes there is a weird

finding in this hair dryer study the hair that was left to air dry had some bulges in the CMC that is the glue that's sticking the cuticle scales together the authors suggest that the CMC might be swollen and damaged when it's wet for too long which led to their conclusion that using a hair dryer is less damaging than air drying this hasn't been replicated as far as I know and I don't think that explanation makes a lot of sense they use 20 cm long human hair which is about this much which is about a year

and a half of growth so you would expect that all of the hair would have been washed and air dried at least 30 times before it was collected and then used in the study but only the air dry sample had bulges so I suspect that something else happened to the hair like maybe that sample came from someone who had a lot more sun exposure or something unusual happened during the study so I just don't think the idea that air drying is more damaging is really supported by their results although air drying does leave your hair

in a wet fragile state for longer which shouldn't be a problem in this lab setup I think I've quoted them before on this before I knew as much about hair science and before I really had the confidence to interpret these studies more critically so I have changed my mind on this sorry I am human I get stuff wrong now damage isn't the only thing to think about sometimes hair damage is worth it bleach is one of the most damaging things you can do to your hair I have bleached my hair from black to white three

times and I'm going to keep doing it but I think it is important to know what the risk actually is so you can work out whether it is worth it for you so here are some of the things you might want to consider apart from damage first off styling you might have noticed that washing resets your hair's shape and like hair strength this is because of bonds hair is held in a particular shape by permanent and temporary bonds again this is like glue when your hair gets wet water comes in and breaks a whole bunch

of of hydrogen bonds if you then keep your hair in a particular shape as it's drying the new hydrogen bonds that form will hold your hair in the new shape but when you wash your hair water again comes in and breaks the hydrogen bonds the permanent bonds pull your hair back into its original shape so that's what you get when it dries unless of course you hold it in some unnatural shape again your hair also slowly goes back to its original shape over time even if you don't wash it that's because heat and humidity will

also break temporary bonds different techniques work best to get particular styles and some of these like blow drying will work better if you use heat to dry wet hair yes this is another lovely diagram from my very nicely illustrated book The Science of Beauty which should be available by the time this video is out the link is on the screen and in the description this video is based on some of the info in it I think you'll really enjoy this if you want science-based practical advice I also debunk a whole bunch of common myths in

it it covers hair obviously but also skin nails makeup and general beauty things like reading ingredient lists what the risks are with specific ingredients sustainability so many topics including dandruff if your scalp is prone to dandruff it might also be a good idea to dry quickly which means using heat one of the big contributors to dandruff is an overgrowth of a fungus called malassezia furfur this is naturally on your scalp but it can cause issues when there's just too much air drying leaves your scalp damp for longer which is perfect for this fungus to grow

and it is even worse if your hair is wet and then you trap the moisture you slow water from evaporating even more with something like a hat or a helmet you might also want to consider this even if you don't have dandruff but your scalp is irritated overgrowth of this fungus can cause irritation before any visible dandruff actually shows up and of course there is the question of time and effort and where things fit into your routine microfibre hair towels and turbans can really help speed up drying with minimal effort and minimal damage these are

made of a water absorbent material that can form hydrogen bonds and it goes through a special extrusion process to create a really big surface area the way towels work is you touch the towel to your wet hair and the water has two choices it can stick to your hair or it can stick to the towel if the towel has more hydrogen bonding sites that aren't already holding onto water compared to your hair then the water will stick to the towel the really big surface area on these towels means that you have more of these exposed

hydrogen bonding sites basically there are more hands for water to grab onto hydrogen bonds are so underrated they explain like everything I love hydrogen bonds you can quote me on that blow drying is more effort and potentially more damaging because with the heat depending on how you do it but it is faster and on the scale of things that damage your hair it's really not on the same level as like oxidative chemical treatments like bleach and permanent dye there are also wet to dry straighteners that are meant to combine drying and styling in the one

step a lot of these claim to be less damaging some of them even claim they cause no damage they use things like lower temperature plates hot air sensors that adjust the temperature in real time I think some of these do seem like they'll be at least a whole bunch less damaging than using a regular straightener on wet hair but I don't think they're likely to be less damaging than gentle blow drying or just air drying but they are faster and more convenient so again it's a compromise so at the end of all of that here

are the key points air drying using a hair dryer on low heat and gentle towel drying are probably the least damaging ways to dry your hair when your hair is wet it is more prone to mechanical damage so if you're going to be rubbing your hair against something like a pillowcase it's probably going to be best to dry it as much as you can first as well as damage you might also want to think about time effort hairstyle and scalp irritation or dandruff so this is my personal compromise let me know what yours is I

try to wash my hair a bit earlier in the day I avoid washing it after about 7:00 p.m. because bleached hair holds onto water a lot better and so it needs a lot more time to dry properly if I go to bed with my hair damp my hair dries rough and bent and it gets damaged I can literally see more split ends the next day I blot it with a normal towel and then I squeeze and wrap it with an Aquis microfiber towel for about 5 minutes I can't really leave this too long because it

makes my fringe dry in a weird way and I cannot style my gringe for the life of me without properly wetting it and letting it air dry in winter it takes longer for my hair to dry and dandruff is usually worse in winter for like everyone I don't really get much dandruff anymore but I do get scalp irritation so I dry the hair around my scalp with a hair dryer I'm still using the Panasonic one that I talked about in this sponsored video it has a scalp mode that is the perfect temperature for not hurting

my scalp then I let my hair air dry if it's still damp a few hours before bed then I will use my hair dryer again which has really good heat control I move it around a lot to try to dry it evenly and avoid hot spots I try to do this early so it still has tons of time to dry properly and then if it still isn't properly dry and I need to go to bed then I will blast it again there are so many myths about hair online I debunked a whole bunch of these

recently in this video my book also debunks a whole bunch of hair myths the link is on screen I have a whole bunch of beauty science videos my hair science playlist is here for your viewing pleasure