Saturday, March 13, 2010

Chemistry of skin: Stratum corneum lipids

If you've just joined us, please check out this post on the chemistry of your skin before reading onwards...

If we think of the corneocytes in the stratum corneum as "bricks", then the stratum corneum lipids are the mortar. (The water soluble natural moisturizing factor is found inside the corneocytes; the lipid soluble stratum corneum lipids are found outside the corneocytes.)

They make up about 15% of the dry weight of the stratum corneum, and contain about 40% to 50% ceramides, 20% to 25% cholesterol, 15% to 25% fatty acids (those with C16 to C30 chain lengths, with C24 to C28 being the most common), and 5% to 10% cholesterol sulfate.

The lipids are arranged in a highly organized lamellar arrangement (fine layers alternating between different materials) with small amounts of water present. This is considered to be a very effective barrier to trans-epidermal water loss (TEWL). Water trying to escape the through the stratum corneum would have to navigate a complicated maze through the bilayer and the corneocytes to get to the surface of your skin - so the lipids and corneocytes make this a much harder task!

The ceramides in our skin are a major component of the structural organization of the lamellar bilayers. There are nine different types offers something to the organization of our stratum corneum and cohesion of the skin barrier. There is a subclass of ceramides called acylceramides, which are ester linked to hydroxy fatty acids, specifically linoleic acid - hence the concept that an oil high in linoleic or gamma-linoleic acid can help improve our skin's barrier properties. In the winter, the ratio of the EOS-oleate increases which means the EOS-linoleate decreases; this happens with dry skin as well. This has a dramatic effect on lipid organization. (The EOS means it is linked to sphingosine.)

We need to treat the stratum corneum lipids well because without them, we end up with really dry, perturbed skin. Particular solvents (hexane, toluene) can damage the lipids and leave our skin defenceless. Harsh cleansers can also mess up the lamellar structure, leading to serious changes in the health of our skin.

So again, mild cleansers for our skin with moisturizers and film formers are always a great idea. Following up cleansing with some kind of lotion is also a good idea. Limit your use of hand sanitizers - the alcohol is very dehydrating. If you really want to use anti-bacterial stuff, try the new ones with benzalkonium chloride or use a really nice cold process soap purchased from your local soap-maker. And follow up with a lovely lotion.

Oils with linoleic or gamma-linoleic acid are always welcomed by our skin (like sunflower, sesame seed, borage, evening primrose, rice bran, and others), especially in the winter. And any oil that creates an occlusive barrier is welcome! Keep your hands out of the toluene - not really that hard to do! - and try to stay well hydrated by drinking lots of water and other fluids.

Join me tomorrow for mechanisms of trans-epidermal water loss!

2 comments:

Warner said...

Hi. I was wondering if you could either tell me what oils have ceramides or point me to a resource for that information. So far I have only been able to determine that wheat germ oil, hemp oil, and rice bran oil contain ceramide. I am sure I am wrong. I am using a product that claims to contain multiple oils that are rich in ceramide but I can't find any evidence that it does. If this product contains lots of ceramide it will be helpful to know so I can identify how ceramide affects my hair. So far I am not experiencing what it promises and would like to make my own.The product I am referring to is Hydratherma Naturals Daily Moisturizing Growth Lotion- It's ingredients are: water, Shea, hydrogenated almond oil, olive oil, Emu oil, peanut oil, emulsifying wax NF, macadamia seed oil, coconut oil, fragrance, Germall plus. Any help you can provide is greatly appreciated. If you can provide a list or source that will show me what oils contain ceramide I would be greatful.

Susan Barclay-Nichols said...

Hi Warner. I did a search on this blog and found a ton of resources on this topic, which you can find here.

Unfortunately, nothing can make our hair grow. And this is a lotion, not a conditioner, which is generally what we use on hair to keep it healthy by reducing friction and combing forces. What do they claim ceramides will do for your hair?