Drying oils are added to paint to help it dry faster. And guess what? They're in several haircare products, too. If your hair normally 'likes' oils but you've noticed your strands feeling stiffer or brittle after using a particular oil-containing product, it could be because that oil is a drying oil.
What is a drying oil?
So what oils are drying oils? Un-natural petrochemicals like mineral oil? Synthetic 'moisture blocking' silicones? None of the above.
Most drying oils are 100% natural, so plant-based and pure you could eat them. They're nutritious, often brimming with Omega-3s and a ton of health benefits. But they can leave your hair feeling like straw.
Some of the most common drying oils you might recognise from the back of your leave in or oil blend: flaxseed oil, hemp oil and soybean oil. Yes, those.
Flaxseed oil is a popular drying oil and can leave hair feeling brittle. Image by alexdante.
This definitely runs counter to the way we're supposed to think about 'good' and 'bad' ingredients in the natural hair community. That simple logic — where natural products, especially oils, are the best thing that could happen to your natural hair, and unnatural ingredients like silicones are bad — it kinda breaks down when the drying oils show up.
But could something as innocuous as cold-pressed flax seed oil really have a worse effect on your hair than the likes of Vaseline? To get why these oils can be so problematic, you need to know a little bit more about them. Here's how they work:
Drying oils: How they dry out your hair
Drying oils don't actively lift moisture from your hair, like a wicked short chain alcohol would. What they do instead is dry on your hair. While water dries off your hair, turning into vapour and floating away, drying oils are different. They dry by oxidising or reacting with oxygen in the air, and they stick around.
The oils have a unique chemistry that allows them to do this. They're all high in unsaturated fatty acids with one, two, or three double bonds like oleic, linoleic and linolenic acid, all on one molecular chain.
From the top, oleic acid, linoleic acid and linoleic acid, fatty acids in drying oils. Ben Mills
As they oxidise, these unsaturated bonds crosslink, forming a tangled 3D network. The result is a hard coating that forms relatively quickly and sets on the surface.
Ever notice a viscous, sticky layer around the rim of a bottle of flaxseed oil you've had for a while? That's the oxidised version of the flax oil, linoxyn. Exposed to air, flax seed oil dries up. It eventually becomes a gummy solid, almost like an extra seal on the rim.
This is exactly why oils like flaxseed oil are used in painting. On its own, paint takes forever to dry, so to speed up drying time, painters mix in drying oils. Once they're exposed to air, and spread into a thin film over a surface, the oils become hard and tough and somewhat elastic.
This tough, protective coating with limited flexibility is perfect for a painting, helping the paint to set before gravity or humidity start moving the artwork around. Drying oils also impart the firm, glossy seal that can make an oil painting last hundreds of years.
But your hair is a different story.
Even though the raw oil you might find in a natural hair product won't have the intense drying power of the boiled flaxseed oil used in industry, that tendency to form a firm seal can leave your strands feeling stiff, brittle and unmanageable.
And hair that's stripped of flexibility and softness is not the only problem: if the oil is drying enough, and you leave it on for long enough, it can also be harder to shift when you try to wash it out.
The tough buildup that drying oils leave naturally becomes more resistant the longer it's exposed to oxygen. If you like to leave oils in your hair for days on end (or even longer), you're increasing the time available for a drying oil to harden on your hair.
The more oxygen a drying oil is exposed to, the stiffer and more stubborn it becomes. Which means you might have your work cut out for you when you do get around to shampooing.
What are semi-drying oils?
Every oil has its own drying rate, depending on the ratio of different fatty acids it contains. Scientists measure this using the oil's iodine value -- the amount of iodine 100g of an oil can absorb. Drying oils like flax seed oil have a high ratio of polyunsaturated fatty acids and so have an iodine value of 130-190+. Article continues below...
Anything under 100 is a nondrying oil, like olive oil, which has mostly monounsaturated fatty acids. Nondrying oils keep their liquid form for the most part.
Right up in between these two, are the semi-drying oils. The iodine values of semi-drying oils range from 100-130. These oils dry more slowly, and never achieve quite the same solidity that drying oils can get. Both rapeseed and sunflower oil are semi-drying oils.
How stiff or dry can drying oils make your hair?
How stiff these oils can make your hair will partly depend on your hair's own natural elastic modulus - or stiffness factor. If your hair isn't naturally very stiff, then drying oils won't have as dramatic an effect. But the higher your hair's modulus, the more likely it is that these oils will leave your hair feeling dry and stiff.
And if your hair is already low on moisture, the effects of a drying oil will be more obvious.Much of our hair's flexibility comes from its water content. Hair that is undermoisturised is already brittle; using drying oils on it will multiply that brittleness.
Using drying oils on hair that is undermoisturised will increase dryness and stiffness. Image by Mwabonje.
Another factor that affects how stiff or dry a drying oil will make your hair feel is time. The longer you leave it in your hair, the drier your hair will feel, as the oil oxidises, creating a barrier that's increasingly tough, and difficult to penetrate.
How can I wash oils out of my hair?
Non-drying oils like olive oil don't harden when exposed to air; they stay much closer to their original liquid form. These oils tend to wash out easily, even with co-washing.
Depending on how often you wash your hair, semi-drying oils like sunflower oil oil may not have time to build up that strong cast that gives a lot of people stiffness and buildup.
You can remove these oils with a mild cleanser, use Baba de Caracol Sulphate-Free Shampoo. Even drying oils take a while to set on your hair, so if you're washing frequently and only using small amounts, they may be less of a problem to remove. With low usage and frequent washing, you should be able to remove them with a gentle shampoo, just like with semidrying oils.
Now this is the worst case scenario: say you've used a drying oil and left it in for quite a while. Maybe your hair was in a protective style, and you didn't really pay it any mind. Now, you notice there's a firm residue on the surface of your hair, it feels dry and almost glued together in some places.
In this scenario, you'll definitely need to clarify your hair — with shampoo. But first, gently prise the hair apart; it needs to be detangled before it's washed or you could make the tangles worse and inflict breakage.
If there is major matting, use a detangling leave in with tons of slip like La Aplanadora Leave In first. That will help separate the strands which the drying oil can knit together. Work your leave in through the tangles one by one; you'll need to make sure they are all out before you clarify.
Once you've detangled, use a clarifying shampoo like atrActiva Anti-Stress Shampoo to remove the drying oil build up. Be warned though: if the film has properly set, you might not be able to get all the residue out in one go.
I'm not using a drying oil. Why is my hair still dry?
Drying oils aside, one common reason why oils can cause dry hair, is using oils on dry hair. A lot of people use oil as a moisturiser, but no oil can do that job.
Moisture only comes from water. If you apply oils on dry hair, then even the silkiest, most softening, non-drying oil could leave your hair feeling dry. That's because even nondrying oils create a hydrophobic film that can lock out a lot of hydration.
Using oil on dry, dehydrated hair is only going to make it greasy and drier. So unless you're doing a pre-shampoo oil treatment, only apply oil on wet hair, damp hair or hair that has been moistened with a water-based product. Using oils this way should help you seal in moisture and get soft, hydrated results.
Is coconut oil a drying oil?
Coconut oil is not a drying oil; it doesn't have the right chemical structure. Coconut oil is composed mostly of saturated fatty acids, while drying oils have higher percentages of unsaturated fatty acids.
Even though it's not actually a drying oil, lots of people do notice that coconut oil dries out their hair. The reason for this is not known, but there are some clues.
The dry, brittle feeling could be related to the fact that coconut oil is one of very few oils that can actually penetrate the hair shaft, due to its high presence of straight chain fatty acids.
Once inside, it binds to your hair's own proteins, making their bonds stronger. This should strengthen your hair -- and studies show it does-- hair treated with coconut oil shows less protein loss after washing.
So why does it make some hair brittle? Could it be because coconut oil makes hair more hydrophobic? Or because the presence of the oil inside the hair shaft makes individual strands feel thicker and stiffer?
Coconut oil is not a drying oil, but does leave some hair dry and brittle. Image by Jonas Ducker.
The fact that coconut oil increases hair's tensile strength means its stiffness should increase too. For some hair though, too much stiffness can mean a loss of elasticity, which can result in breakage. We see this sometimes with protein treatments, which are designed to strengthen the hair, often by making it stiffer.
If the proteins are too effective at stiffening the hair fibre, the result is increased fragility and breakage, even though the product is supposed to make hair stronger. This over-stiffening effect might be the reason people report dry hair after using coconut oil. But that doesn't make it a drying oil — nor does coconut oil does contain protein, in case you were wondering.
What if all oils make my hair stiff and dry?
Oils don't have to be drying oils to make your hair feel dry.
For some hair, especially extremely low porosity hair, most oils can stiffen strands, making them feel crunchy or rough, whether you apply them on wet hair or not. This could be because the oils can't bind well to the resistant cuticle on low porosity hair.
On these hair types, nondrying oils can cause many of the same problems as drying oils: buildup, roughness, dehydration and even extreme breakage. If this sounds like your hair, it's probably time to stop force-feeding your hair oils.
Water-based rather than oil-based products might be the answer if every oil might as well be a drying oil to your hair.
How do I know if an oil is a drying oil or not?
As well as the popular drying oils we've mentioned in this article, there are tons of other drying and semi-drying oils; too many to list here.
If you want to be able to spot drying oils that aren't covered in this article, just download our Drying Oils guide. It breaks down dozens of popular natural oils into drying, semi-drying and nondrying so you know what you're dealing with. You can get it here.