Thursday, March 29, 2012

Formulating for dry skin: Impaired skin barrier ingredients

As the goal of this blog is to set you on fire rather than handing you matches, I thought we'd take some time to look at the ingredients that might benefit dry to really dry skin. 

What do we know about dry to really dry skin? We know that really dry skin probably has an impaired skin barrier, lower natural moisturizing factor, and lower hydration levels in our stratum corneum.

If you have an impaired skin barrier, you're probably experiencing increased transepidermal water loss. When the climate is dry, TEWL increases. When we have too little water in our skin - we want 10% to 20% or so - TEWL increases. When there's damage to our skin - sunburn, burns in general, wounds - TEWL increases. In short, anything that assaults or insults our skin increases TEWL.

What can we do to reduce TEWL? We can stay away from things that damage our skin, like too much sun or wind exposure, extremes in temperatures, or really scratchy sweaters. We can live in a humid climate or have a humidifier in the house (40% to 60% humidity is ideal). And we can make lovely creations that will trap water into our skin or add more when needed.

We want to increase our skin's barrier repair mechanisms and protect it from further damage. We do this by using occlusive ingredients to protect our skin and fatty acids like linoleic acid and gamma linoleic acid (GLA) to speed up the repair process.

All of our emollients - oils, butters, and esters - will trap water on our skin and keep the world out, but there are three ingredients specifically approved by the FDA for this purpose - dimethicone, allantoin, and cocoa butter.

Each of these can be used in an emulsified product, like a lotion or body butter. Use up to 5% dimethicone in the cool down phase, up to 2% allantoin in the heated water phase or cool down phase (I prefer the heated water phase), and up to whatever level you like for cocoa butter in the heated oil phase - but you have to be careful when thinking of including them in other products.

Dimethicone can be used in anhydrous or emulsified products, but you can't use it in a water based product like a toner without some kind of emulsification. Same with cocoa butter - use in anhydrous products, but not in toners or water based products. Allantoin can be used in water based or emulsified products, but you can't use it in an oil based product because it won't dissolve and gritty feeling allantoin is just awful!

So if you want to add some occlusion to your toner, consider using up to 2% allantoin in the heated water or cool down phase. (I don't go over 0.5% but you can go as high as 2%). If you want to add occlusion to your whipped butter without thickening it too much or want some occlusion in a lotion bar, think about using 2% dimethicone. If you want to make your lotion bar a little bit harder, consider up to 10% cocoa butter in that product. And so on.

We really want to include some nice emollients that will help repair our skin's repair mechanism do its job, so you want to look for oils that contain linoleic acid or gamma linoleic acid, like soybean oil and rice bran oil (linoleic acid) or evening primrose and borage oil (GLA). Look for higher levels of phytosterols, which can soften skin and reduce transepidermal water loss. Oleic acid is a good fatty acid for softening and moisturizing skin, but it isn't going to give you the skin barrier repair mechanism speed up that you'll get from the other fatty acids.

My first choice for dry skin would be soybean oil. It's filled with Vitamin E, phytosterols, and linoleic acid. It's inexpensive - one of the most inexpensive oils, in fact - and it's easy to find. The one down side is that it is a little on the greasy side. Rice bran oil, sesame seed oil, and sunflower oil are also great choices. If you want something a little less greasy, you could go for an oil like evening primrose or borage oil, both of which are definitely less greasy, but they are much more expensive than the usual carrier oils. If you want a less greasy carrier oil, you're in a bit of a bind because most of them contain more oleic acid than linoleic acid. My suggestion is to make your products less greasy using something like IPM at up to 5% in the heated oil phase or use an emulsifier like BTMS-50 rather than give up the awesome power of the linoleic or gamma linoleic acid.

You don't really want to use anhydrous products, like lotion bars or whipped butters, on really dry skin. WHAT? DID YOU REALLY JUST SAY THAT? Follow along with me for a moment...

Yes, they moisturize - oleic acid is a great fatty acid for softening our skin and linoleic acid is good for speeding up skin's barrier mechanisms - but if you don't have a lot of water in your skin, what is the anhydrous product trapping? Anhydrous products can prevent further transepidermal water loss and they can soften skin and help repair the barrier mechanisms of our skin, but they aren't going to trap in water if there's none there. This is why you want to apply a body oil, anhydrous body butter, lotion bar, whipped butter, balm, anhydrous facial serum, and so on onto dry skin after making it damp. This gives the product something to trap against our skin! (Generally you'd take a bath or wash your face to get your skin damp, but spraying it with water - or something like a toner - works just as well!)

Join me tomorrow as we take a look at how we can increase the hydration of our stratum corneum in dry skin!


Anonymous said...

Great Post. Love it.

Tara said...

How about using beeswax to trap in the moisture and resist wash-off? What percent would you recommend for this? I know you once did a stellar trashed hands lotion with a bunch of very occlusive ingredients, but I am having trouble finding it. That and a very moisturizing hand wash. My hands are desperately in need of some therapy :-(

Valerie said...

I agree that putting an anhydrous product on dry skin usually does not help much but I can think of at least one exception.
I have very dry, sensitive hands that will often crack and bleed if not cared for. Before bed I wash my hands then immediately apply shea butter or a blend of butters (or petroleum jelly if nothing else is available.) I then put on a pair of white cotton gloves which I wear overnight. This regimen helps more than any lotion ever has.

Susan Barclay-Nichols said...

Hi Tara. Could that have been the hemp hand protectant duplication? If so, it was a rice bran version I did for the lamentably short lived Iron Chemist series. I'll do a search for it in the morning and post a link, if it's the right one!

Hi Valerie! You made my point! It's best to make our skin damp before applying the anhydrous product. You mention you wash your hands before applying your product and wearing gloves - exactly my point in the post! So it's not an exception: It's what I recommended!