Sunday, July 24, 2011

Riffing on silicones

Silicone, it's in shampoo, conditioner, hair styling products, skin lotion and creams. Lately it has come into vogue to eschew silicones completely. Think that one through first, because you might be needlessly limiting yourself. Silicone myths: "It suffocates your hair." "Silicones prevent water from getting into your hair, so it gets dehydrated." To which I say: A) Hair doesn't breathe, suffocation is not an issue. B) Silicones do keep water out, but they also keep water in. ©Science-y Hair Blog 2013

Commonly you'll be looking at some form of dimethicone or "silicone oil." Other common silicones are "silicone polymers" or ("siloxanes"). If you pour dimethicone, it is thick, clear, somewhere between "tacky" and "slimy" feeling. It does not rinse off surfaces easily. When wet, it can be wiped off a nonporous surface with some force, but when dry a detergent and scrubbing is required. Silicone ingredients do not tend to irritate the skin. But they don't necessarily wash off easily, which is fine on skin because we're constantly shedding skin cells. Kind of makes you want to go wash the floor, right? Not all silicones are this viscous, some are quite watery.
Silicones are added to skin products to seal in moisture and help the product spread over the skin easily. To hair products, silicones thicken, improve distribution of other ingredients, coat the hair for shine and decreased friction (making hair easier to comb and more resistant to tangles), and adds water resistance.©Science-y Hair Blog 2013
Silicones bond to the hydrophobic (undamaged) portions of hair in particular (1). Less friction means less damage to hair and thus stronger hair. Reduced water loss also improves hair strength.
©Science-y Hair Blog 2013
Should you use silicones or avoid them?
Avoid them if: 
-You do not wash your hair with any sort of shampoo. Silicones don't rinse off, they accumulate and you'll end up with heavy, limp hair.
-You have very fine or thin hair that tends to get weighed down easily.
-You don't like the way they make your hair look and feel.

Leave it to cosmetic scientists (one of my Chemistry professors told a class that the money in Chemistry was in cosmetics and petroleum... and he wasn't kidding) to figure out how modify silicones to allow them to rinse off more easily. A chimera of the water-soluble and water-insoluble - the water-soluble silicone!
©Science-y Hair Blog 2013
Chemically attach a water-soluble ingredient like Polyethylene glycol or a protein to a silicone and now it has a polar end. That polar end (which would prefer to rinse away with water because "like dissolves like") helps drag the silicone away with rinsing or cleansing. So you get the benefits of silicone and none of the residue, or at least far less. If the silicone is attached to a protein, even better because proteins bond to the damaged parts of your hair - so the undamaged parts get a dose of silicone-protection and the undamaged parts are protein-enriched.
©Science-y Hair Blog 2013
How do you find water-soluble silicones? It would be nice if it were on the front label so we'd spend less time squinting and scowling at labels in the drugstore. Here are some to look for: 
Anything with a PEG-# preceding the "silicone" such as PEG-12 Dimethicone and:
Silicone Quaternium-8
PEG-7 Amodimethicone
Dimethicone PEG-8 Phosphate
PEG-8 Disteramonium Chloride PG-Dimethicone
Dimethicone-PG Diethylmonium Chloride
Hydrolyzed Silk PG-Propyl Methylsilanediol Crosspolymer
Hydrolyzed Wheat Protein Hydroxypropyl Polysiloxane
Dimethicone PEG-8 meadowfoamate
Dimethicone Copolyol
Lauryl Methicone Copolyol
Lauryl PEG-8 Dimethicone

A while ago, I tried spreading different products on a piece of smooth glass, then rinsing them with plain water and, in some cases, some gentle rubbing.
The products which included PEG-12 Dimethicone did rinse off with some extremely light agitation (rubbing very lightly under the tap). 2 products containing dimethicone did not rinse off with water or rubbing and required a detergent - although glass is unlikely to bond with any of the ingredients whereas hair can have far more interactions.
©Science-y Hair Blog 2013
Water-soluble silicones are making an appearance in skin products as well, although the potential for irritancy increases with the addition of other ingredients and the processes whereby that happens.
©Science-y Hair Blog 2013
Update: A 1994 article in Skin Pharmacology and Physiology by Rushton et. al. reported a couple interesting things.
1) Silicones (from a silicone-containing 2-in-1 shampoo) accumulate on the surface of hair for the first 5 uses, but after that, there was no accumulation. There is only so much surface on the hair for silicone to bond to, it does not accumulate indefinitely.
2) 90% of silicone residue was removed with one shampooing with a silicone-free shampoo. The detergents sodium lauryl or sodium laureth sulfate, ammonium lauryl or laureth sulfate and cocamidopropyl betaine (possible cocobetaine) are the ones to choose for removing silicone residue.

Koyanagi, A. 2007. Journal of Cosmetic Science 58: 435-441


  1. Can silicones be suitable for medium to coarse porous kinking hair if you want to reduce friction and tangling?

    1. Silicones are designed to provide gloss and are excellent at reducing friction. Much depends on the formulation of a product. For example, silicones in a shampoo reduce the friction that occurs during washing (which is a lot). Silicones in rinse-out products help those products lubricate when the hair is wet *and* dry and the same for leave-in conditioners. Sometimes silicones are even more effective when used together with natural (plant) oils. In my opinion, if you want lasting friction reduction - stick with the silicones that don't evaporate - usually preceded by "cyclo." Use the search function in the upper left of the blog and you'll find a post on silicone solubility with more information.

    2. I'm wondering: are silicones less likely to attract lint than oils?

    3. Silicones and oils both accumulate dust and lint. Silicones are not polar (nonpolar), they don't have a charge so they don't actually attract dust and lint, but dust and lint may stick to the silicone in your hair more firmly than to hair with no oils or silicones.

      Most oils are mostly nonpolar polar, so they do not attract dust and lint, but they are more likely to stick to an oil in your hair. Oils that contain triglycerides or fatty alcohols (coconut oil, palm kernel oil) and esters (jojoba oil) have some polarity and are more likely to attract dust or lint to your hair.

      So it's worth trying to avoid coconut oil, palm kernel oil and jojoba oil on your hair to see if you get a reduction in lint. If those oils (or silicones) are covered with a layer of another hair product, they have less exposure to dust and lint.