Updated: June 2016

Plant oils are emollients used to soften hair or add “plasticity” or pliability. Pliable hair bends easily without breaking. Hair with oils applied to it lines up better with neighboring hairs thanks to the lubricating properties of oils (slip). Oils generally increase glossiness. When water is able to get inside the hair easily, it swells on the inside. But the cuticle layer on the outside cannot expand, so the cuticle scales are forced to stand up - a position in which the cuticles are easily broken and the hair is more porous. Oils which penetrate into hair make the hair proteins more hydrophobic (water-repelling). Healthy, strong hair is naturally hydrophobic. Normal and lower porosity hair is somewhat hydrophobic. Hydrophobicity (water-repelling) is a matter of balance. What we don't want is for our hair to take on too much water, too quickly. That's the problem. Hair gets dehydrated. Re-hydrating hair is a good thing. But when hair is porous, it takes on more water than is good for it, too quickly and that's when the swelling occurs.



Almost any oil will help repel water, but they do it either by sitting on your hair as a film, or by soaking in slightly - penetrating the hair shaft.



Can we completely predict the behavior of any oil in any given person's hair? Seems doubtful. Please don't look at this chart and decide certain oils are not for you try them first. You never know what your hair is going to like without giving it a chance. This chart is organized with oils that have been demonstrated to penetrate hair at the top (green). You'll notice that they either have polar triglycerides or else high percentages of monosaturated fats.

©Science-y Hair Blog 2013

If you have dry, porous, rough-feeling, or coarse hair, you may love the penetrating oils. If your hair has become porous from environmental damage (sun, heat, hot styling tools, wind), you will probably like some penetrating oils at least on the ends of your hair. If you have fine or soft hair which is easily over-conditioned, those same oils may make your hair feel greasy and lank unless used in very small amounts. Lower porosity hair may do better with blends of penetrating oils and less-penetrating oils.



Triglycerides and hair penetration:

One key to whether or not an oil penetrates into the hair is the amount of triglyceride and short-chain fatty acids it contains – as well as how the components of the triglyceride are arranged. Lipid molecules need to be small to penetrate into hair – less than 18-20 carbon atoms, but that's not the only variable. Oils are not composed merely of one kind of fat (let’s call them lipids because it sounds prettier) – they’re composed of many different lipid “ingredients.” Triglycerides in oils are 3 fatty acid molecules attached to a glycerol “backbone.” The short-chain lipids – even if they are not triglycerides - are usually straight chains with no branching bits, making them small, compact

Additionally, triglyceride components in plant oils can be polar (slightly positively charged) and that allows them to be attracted to the polar (negatively charged) proteins in your hair. Usually oils are non-polar and this is a big difference in chemistry to have an electrostatic (+ and -) interaction versus just having some oil form a film over your hair! This helps those triglycerides be actively pulled through the cuticle-membrane complex over your hair shafts to the inner portions.



Fat saturation and oil penetration of hair:

In addition to the above and as a rule of thumb, monounsaturated fats tend to be better at penetrating your hair than polyunsaturated fats. What that really means is that these small, compact (non-branching) molecules penetrate the hair more deeply whereas larger lipids referred to above may only reside in the cuticle layers of your hair or on top because they are less compact and more branching. If your hair needs a great deal of softening and protection from swelling in water, the deeper-penetrating oils are a better choice. But if your hair is easier to maintain in good condition, having oils that only reside in and on the outermost cuticle layers is still going to give you benefits.



Which fatty acids to look for?:

Oils are composed of differing amounts of fatty acids. Oils which penetrate hair tend to contain larger amounts of fatty acids like lauric acid, caprylic acid, palmitic acid, myristic acid, oleic acid, or linloeic acid.



How to use this chart: 1) At the top of the chart are oils that have been demonstrated in lab tests to penetrate the hair, and which should, based on their chemistry - those oils are highlighted in green. They are high in triglycerides and/or contain monosaturated lipids which can penetrate below cuticles. 2) Below that are are oils with some penetration (highlighted in blue) - including olive oil which has been documented to penetrate the hair. These are arranged based on their lipid composition from more likely to penetrate (top of that list) to less likely at the bottom of that list. 3) At the end of the list is oils which do not penetrate the hair based on lab tests and/or their chemistry. They are highlighted in pink. 3) The chart provides percentages of the relevant components of the oils if you are interested.

-Lipids less than 18 carbons long: The percentage of the oil which is small enough to seep under your cuticles.

-Polar triglycerides: The polar triglycerides are the ones that soak in - you want higher amounts of these for a penetrating oil.

-% Monosaturated lipids: Monosaturated lipids are also are more likely to penetrate the hair.

-Pentration improves with heat?: For some of these oils, I have data on this and I reported it.

-Hair penetration documented by research?: Those oils which have been tested in a lab on human hair are indicated here.



Oils with high penetration % Lipids that can “seep” under cuticles Triglycerides Polar triglycerides (these penetrate hair) Monosaturated lipids lipids Penetration improves with heat? Hair penetration documented by research Coconut oil 95% Yes (64%) Yes 6% Yes Yes, excellent Ucuuba butter Yes (~70%) Possibly ~99% unknown Yes, good Sunflower oil 91% 14-40% Yes Yes, good and no, depending on the study Palm kernel oil (i.e. Red Palm Oil 98% Yes (56%) Yes 15% likely Not documented, likely based on chemistry Capric Caprylic triglycerides triglycerides NA Yes Yes Unknown Not documented, but if extracted from coconut oil, should penetrate Babbasu oil ~100% Yes (12%) Yes 16% Possible Not documented Oils with some penetration, in decreasing order (based on lipid composition) % Lipids less than 18 carbons long Triglycerides? Polar triglycerides? Monosaturated lipids lipids Penetration improves with heat? Hair penetration documented by research Castor oil ( Not sure castor oil belongs at the top of the list – triglyceriges are confounding, draw your own conclusions 15% Yes (86-90%) Yes 7% Unknown Not documented. Chemical structure not ideal for penetration but possible??? Olive oil 94% 65-80% Possible Yes, good Avocado oil ~100% Yes Yes 55-75% Possible Not documented Corn oil ~80% Yes (12%) Yes 19-49% Possible Not documented Canola oil 100% 60% Unknown Not documented Mustard seed oil 44.90% 66% Unknown Not documented Sweet almond oil ~99% 70% Unknown Not documented Apricot kernel oil ~100% ~73% Unknown Not documented Argan oil 98% ~45% Unknown Not documented Sesame seed oil ~86% 40-50% Unknown Not documented Shea butter ~98% Yes No ~50% Unknown Not documented Peanut oil ~87% ~55% Unknown Not documented Kokum butter ~100% 39-41% Unknown Not documented Grapeseed oil 99% 12-25% Unknown Not documented Rose hip oil ~97% 15% Unknown Not documented Hemp seed oil ~100% 12% Unknown Not documented Flax seed (linseed) oil 99% 12-34% Unknown Not documented Perilla oil ~99% 12-14% Unknown Not documented Safflower oil 90% 13-21% Unknown Not documented Cocoa butter ~98% ~32% Unknown Not documented Oils with little to no hair penetration % Lipids less than 18 carbons long Triglycerides? Polar triglycerides? Monosaturated lipids lipids Penetration improves with heat? Hair penetration documented by research Rice bran oil 83% 40-50% Unknown No, penetration poor Mineral oil No penetration Jojoba oil less than 1% No penetration Why are less-penetrating or non-penetrating oils are used in products? They add shine, they decrease friction for easier combing and fewer tangles. Not everybody needs oils to soak in to their hair. If you wanted an oil specifically for gloss or shine or lubrication, you do not want it disappearing from the surface of your hair over time.

Oil film on hair obscuring cuticle

details - but adding shine

and lubrication. If this were a hair-

penetrating oil, over time this

coating would thin.



Ways to use oils

1) Oil pre-shampoo! This is one of the best times to use oil, even if it seems counterintuitive to put oil on your hair before you're going to wash it - in part to remove any excess oil. Apply a light (or heavy) oiling to your hair and leave it on for 2-12 or more hours before shampooing or otherwise cleansing your hair. The oil prevents dehydration and loss of proteins and otherwise protects and buffers your hair from water and detergent. If you get the amount of oil and leave-on time right, your hair will be more flexible and feel softer, better lubricated and if you have waves or curls, they will be better-defined. The longer you leave the oil on, the more oil will work its way into your hair.

2) Added to a deep or intense conditioning treatment.

3) To seal damp hair. But in my opinion you can't use just oil and expect your hair to stay hydrated. You need some leave-on conditioner over your oil. Or a nice film-forming gel like flaxseed gel for hydration, maybe a little conditioner. In my hair, just oil or just oil and flax gel gets a little fluffy - some conditioner and humectants (or protein) brings everything back together.

4) Oil rinsing. Either mix 1/4 oil and 3/4 conditioner or 1/2 oil and 1/2 conditioner and use this as you would a rinse-out conditioner, or apply the oil to clean, wet hair, then apply conditioner and squeeze and gently massage the oil and conditioner together in your hair. Then rinse and enjoy the very soft result.

If oils and your hair do not always get along,



If oils and your hair do not always get along, this post may help you out.

When to use penetrating oil pre-wash treatments

-If you notice your ends looking thinner or sparse or light colored or tend to fan or splay out.

- If your hair loses definition (cannot form curls or waves or coils in curling hair or is flyaway and too-light in straighter hair).

- If you have tried deep conditioning and your hair is still dry or not flexible enough.

- You have frizz you cannot manage with styling products, clarifying or chelating products or protein.

- Your hair starts to require more time to dry (penetrating oils cut back on "waterlogging" which means you might have shorter dry-times).







Resources:

Journal of Cosmetic Science, 60, 273–280 (March/April 2009)

Brazilian oils and butters: The effect of different fatty acid chain composition on human hair physiochemical properties. ADRIANA FREGONESI, CARLA SCANAVEZ, LEANDRA SANTOS, AMANDA de OLIVEIRA, ROBERTA ROESLER, CASSIANO ESCUDEIRO, PRISCILA MONCAYO, DAISY de SANCTIS, and JEAN LUC GESZTESI.





Journal of Cosmetic Science, 56, 283-295 (September/October 2005)