Friday, March 12, 2010

Chemistry of skin: Natural moisturizing factor (NMF)

Natural moisturizing factor (NMF) is found within the corneocytes, and makes up 20% to 30% of the dry weight of the stratum corneum. It consists of amino acids (40%), sodium PCA (12%), lactate (12%), urea (7%), ions (18.5%), sugars (like glycerol - 8.5%), and a few other things. These are water soluble humectants (meaning they draw water out of the atmosphere to our skin) that have a huge impact on the biochemical and mechanical properties of our skin. Having an adequate NMF level in our skin can prevent or reduce skin tightness, cracking, scaling, and flaking. It improves our skin's plasticity (thanks to the interactions of the amino acids with keratin) and helps maintain skin's barrier properties.

Most of the amino acid based parts of the NMF are derived from the enzymatic hydrolysis of proteins, filaggrin, and the corneodesmsomes of our skin. (This is actually a process called proteolysis - (Wiki) Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion.)

Filaggrin is a really important protein found in our skin! The degradation of this protein makes it possible for our outer skin layers to maintain an adequate water supply in dry or arid environments. When our skin is occluded or humidity is high, there is a minimal breakdown of this protein. When we are in more arid climates, the filaggrin breakdown increases to produce more NMF. More NMF is a good thing! (We'll get into filaggrin more when we look at the mechanisms of dry skin.)

The contents of the NMF do more than act as humectants. The lactate and potassium can affect the pH and stiffness of the stratum corneum. The lactic acid stimulates ceramide biosynthesis and improves barrier function. The hyaluronic acid (HA - picture to the left) maintains hydration and structural integrity of our skin. It also interacts with intercellular lipids and regulates the mechanical properties of the stratum corneum.

Finally, we come to glycerol (also known as glycerin, one of the sugars found in our skin). It is derived from the breakdown of the triglycerides found in our sebum. It acts as a really awesome humectant in our skin and works well when applied to our skin. Study after study has shown that adding glycerin to our products can only help our skin maintain or increase hydration and enhances our skin's pliability.

So what does this mean for creating our products? Using occlusive and hygroscopic ingredients are essential in our products. Humectants truly are a girl's best friend, and leaving them out would surely be a bad idea. We can use a variety of humectants - sodium PCA, sodium lactate, HA, or glycerin - in all of our products (okay, not in the anhydrous ones, but olive oil works well, too!) and we should be including them in everything we make!

When we cleanse our skin, we can remove some of this NMF, which means we want to use mild cleansers and re-fat our skin afterwards. We can add re-fatting and conditioning agents to our cleansers (like honeyquat or polyquat 7 for the cationic ingredients, and esters, water soluble oils, or things like Crothix or EZ Pearl) to help restore the damage! We can add humectants to our cleansers to ensure we are restoring our skin afterwards (remembering that sodium lactate is rinsed off when we cleanse, so not a good choice). Don't forget the slight occlusive nature of our hydrolyzed proteins (the higher molecular ones like wheat or oat - silk can be low molecular weight and penetrate our skin. Good, but not occlusive!) Dimethicone is a great occlusive ingredient, as well. And we want to use very mild cleansers or add mildness to the mix by using things like Crothix or coco betaine.

When we use a lotion, spray, or other creation, we definitely want those humectants in there. Occlusive ingredients are good - everything from oils and butters to aloe vera, rosemary extract, and allantoin - and there's one for every type of creation! Obviously anhydrous products will be more occlusive than water based ones, but there's no reason not to include the water based ingredients like allantoin, aloe vera, and allantoin in a toner or summer fun spray.

Join me tomorrow for fun with stratum corneum lipids!


Topcat said...

Wow! Learning heaps - thanks :)

Alana said...

Should we not be using occlusive ingredients since it will cause minimal breakdown of the filaggrin and thus water supply will not be maintained? What are some non-occlusive ingredients?

Susan Barclay-Nichols said...

Hi Alana. No, we should be using occlusive ingredients to prevent transepidermal water loss and keep that natural moisturizing factor "trapped in". It's a good thing for the filaggrin to break down when we need it - say, when we're in a hot or less humid place - but we should try to prevent getting our skin from getting to that point by occluding it or using hygroscopic ingredients. Most of our ingredients are occlusive - to write up a list here would take me weeks! - but there's nothing wrong with occlusion. It's something good for our skin, which is why we use ingredients like dimethicone, allantoin, and cocoa butter in our products.