When a surfactant comes into contact with our skin, it can bind to the surface and denature our skin's proteins. It can interact with the lipids on our skin and disrupt the organization of the stratum corneum lipids, which can lead to increased dryness and increased trans-epidermal water loss. Surfactants can remove the natural moisturizing factor in our skin, leading to a reduction in the ability of our skin to attract moisture from our environment. If they annoy our skin enough, the anti-inflammatory response can kick in leading to itching, drying, and redness. (This is one of the reasons you don't want to leave an anionic surfactant on your skin as a leave-on type of product!)
Okay, now that I've scared you into never wanting to use surfactants ever again, let's take a look at how easy it is to increase the mildness of our surfactant mixes so we won't have these horrible side effects for simply washing our faces!
We can increase mildness by...
- using only very mild surfactants;
- reducing the concentration of surfactants in our creations;
- modify the behaviour of the surfactants; and
- protect the skin's surface by including various ingredients.
Using only mild surfactants will create a mild creation. You can create some very mild cleansing products using decyl glucoside (non-ionic) with cocamidopropyl betaine (amphoteric), which we see in baby products. We can create very mild blends with anionic surfactants (see below), then combine them with the non-ionics and amphoterics to creating something even milder!
If you want to try making something without anionic surfactants, you could make a really mild blend using decyl glucoside, cocamidopropyl betaine, and PEG-7 cocoate that will re-fatten the skin, thicken quite well, and offer mild cleansing with not-so-great foam. This would work well as a very mild facial cleanser or make-up remover, but for something like a body wash, we really do need our lovely anionics.
I like using a combination of SCI, cocamidopropyl betaine, and DLS mild for very mild cleansing. Combine this with some of the ingredients I'll mention in the next sections, and you have yourself a very mild cleanser with great foam and fantastic skin feel.
Reducing the concentration of the surfactants in our creations is really simple. Just use less. I know, this sounds really glib, but it's true. If you are making a facial cleanser, but find that it's a little too much for you, you can take that mixture, add about 33% more water and turn it into a foaming cleanser - if you don't want to thicken it - or add some more Crothix or salt and thicken it up!
Combining surfactants is a great way to modify the behaviour of the surfactants in our products and it's a really simple way to increase mildness. Adding cocamidopropyl betaine (amphoteric) or non-ionic surfactants like decyl glucoside or even polysorbate 20 will reduce the potential irritancy of an anionic surfactant dramatically, and you can combine surfactants to increase mildness. There are two theories about why this works.
Theory one: Surfactants tend to form micelles when they are added in proper concentration. Some surfactants aren't that keen on joining the group and they float around in the water as monomers (polymer means many, monomer means one - they're loners). These monomers are what bother your skin and cause irritation as they interact directly with your skin's proteins. When we add a few surfactants together, they form larger and more stable micelles, which reduces the number of monomers, which reduces the irritation.
Theory two: Surfactants compete for binding sites on your skin. When you add a milder, secondary surfactant it occupies the spot to which the first, less mild surfactant could have bound. So the less mild surfactant has no where to attach to your skin and is washed away.
A little more chemistry...when the polymers interact with the micelles, the micelles become more hydrophobic. Increased hydrophobicity means less adherence of the surfactants to your skin. We know that adherence of surfactants to your skin is a key element in that feeling of tightness after washing, so less adherence equals less irritation.
We can add polymers, proteins, and emollients like dimethicone to our products to increase the mildness and help protect our skin. When we add a polymer - like polyquat 7, honeyquat, or dimethicone - they incorporate into the micelles and reduce the relative amount of monomers in the solution. As the monomers are the culprits in causing irritation, this will reduce irritation. As well, they compete for those binding sites so the less mild components of our cleanser will wash away.
When we add proteins, we want to add the higher molecular weight proteins like oat or wheat to form a film on our skin. Silk is lovely for dry skin types, but if it penetrates your skin, it kinda defeats the purpose of forming the film. Proteins are great additions to surfactants mixes - they increase foam stability and density and increase the feeling of creaminess and slipperiness.
Note: If you can't get proteins, then cocamidopropyl betaine is a great alternative!
Emollient ingredients - Crothix, glycol distearate, water soluble oils, fatty alcohols (like cetyl alcohol), and silicones - will help reduce the disruption of the stratum corneum lipids, which can lead to an impaired barrier function. You can use a lotion after bathing, or you can incorporate some of these ingredients into your surfactant mixes. (I'll be going over the specifics of Crothix and glycol distearate in the upcoming posts on increasing viscosity in our products. For now, click on the links for more information).
This is what we're seeing a lot of in the moisturizing body washes. Generally they'll use mineral oil with an emulsifier as the emollient, but you can use a variety of different ingredients to get that same effect. I like using water soluble oils - I have sunflower, jojoba, and olive oil - at about 4% for adding moisturizing.
And don't forget your humectants! One of the big problems with incorporating humectants into your surfactant creation is this - they wash off. Sodium lactate is pointless in a surfactant mixture because it'll wash off and fail to offer any form of humectancy! Glycerin and urea (in urea form or Hydrovance) are your best choices for humectants, as well as one of the glycols like propylene or butylene glycol. Glycerin not only increases your bubbles and lather - bonus! - but can help with barrier repair, improved stratum corneum hydration, and reduces trans-epidermal water loss. I add it at 3%, but you can go even higher to 5% - 8% in a body wash if you have really dry skin. Most of this will wash off, but if you get even 1% to stay on, that's a good thing!
Finally, we can include some anti-inflammatory ingredients - like aloe vera, witch hazel, white willow bark, or salicylic acid - but it's better to reduce irritation than to treat it after the fact!
If you take a look at my basic body wash recipe (which we'll be modifying like silly over the next week or so), you'll see I have tried to include every single feature listed here.
BASIC BODY WASH RECIPE
15% cocamidopropyl betaine
15% Amphosol AS-90 or SLeS - mild anionic surfactants
15% BSB or LSB - gentle anionic surfactants
5% aloe vera - film former
3% glycerin - humectant
3% Condition-eze 7 - cationic polymer
2% cromoist or other hydrolyzed protein
2% panthenol - great humectant, skin barrier repair
1% fragrance or essential oil
1% liquid Crothix - re-fattening our skin
Colouring, if wanted
Join me tomorrow for more fun with surfactants!