How is dry skin defined? It is when your skin is a dull colour (gray to white) with a rough texture and an elevated number of ridges. When the equilibrium of the stratum corneum is out of whack, the skin's ability to maintain hydration is decreased, and skin is more susceptible to environmental factors because the skin barrier is impaired. Trans-epidermal water loss increases. Desquamation is abnormal, with skin coming off in sheets instead of cell by cell, so your skin looks rough and dry, and you get that white or ashy look.
Dry skin could be genetic, or it could be the result of over exposure to UV radiation, solvents, chlorine, detergents, or excessive amounts of water, all of which can lead to a disturbance in the stratum corneum lipids. This means water can escape faster through your skin, leading to a reduction in hydration. The ceramides in your skin are also messed up, which reduces the barrier properties. The increase in TEWL and the reduction in barrier properties means your skin will get drier and drier until the situation is improved!
If these things weren't bad enough, the reduction in your skin's natural moisturizing factor makes the situation even worse! NMF is derived from filaggrin: 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 we're in a low humidity environment, the NMF production increases. If it doesn't, our skin gets drier. If your skin is already too dry and poorly hydrated, the NMF fails to increase in arid environments, which only increases the level of dryness!
Hyaluronic acid is found in the middle spinous layer of our skin, not in the stratum corneum or stratum granulosum. Its role in skin hydration is not completely known, but it is a very powerful humectant that can bind a thousand times its weight in water and it does help our skin in retaining said water for hydration. Older and dry skin is characterized by lower levels of HA. (And as a note, so far studies are showing that topical application of HA won't penetrate your skin to increase the amount in the stratum spinosum, although it will make your stratum corneum feel nicer.)
And we come to aquaporins. Our epidermis contains aquaglyceroporins (AQP3), which are proteins embedded in our skin's cell membranes that allow for the transport of water and glycerin into our skin. AQP3 is thought to enhance trans-epidermal water permeability to protect the stratum corneum from water evaporating through the skin and/or to spread water throughout the layer of the keratinocytes.
Mice deficient in AQP3 show reduced stratum corneum hydration, impaired skin barrier recovery, delayed wound healing, altered skin elasticity, and reduced glycerol in the stratum corneum due to the impaired glycerol and water transport to the epidermis. In short, an impairment in AQP3 leads to a reduction in the water holding capacity of our skin.
When our skin has been exposed to too much sun, we find decreased water permeability in cells, impaired cell migration (meaning new cells aren't moving to the stratum corneum), and delayed wound healing, all thanks to impairment in the AQP3.
Dry skin also sees an increase in pH, which is not a good thing. Various proteases involved in the desquamation process don't work well when the pH is increased, so we see less turnover of the top layer of cells! As well, our skin is less resistant to chemical and microbial attack.
So how can we treat dry skin with our lovely creations? As always, we need to use mild cleansers with very mild detergents. As much as I love surfactants, they can remove the stratum corneum lipids and reduce the NMF from our skin. Luckily, most surfactants are mild, and there are tons of ways to increase mildness in those types of products.
Because the skin's barrier mechanisms are probably impaired, we want to use a lot of lovely oils with good fatty acids, cholesterol, ceramides or glycerol, those things that make up the stratum corneum lipids. You'll want to apply these lovely lotions two to three times a day and especially after bathing to trap in the moisture.
If you are suffering from dry skin thanks to too much sun exposure (current or past), you likely have an impaired skin barrier, lower NMF, and lower hyaluronic acid levels. Unfortunately, adding HA to your creations isn't going to change this as it won't penetrate to the stratum spinosum level, which is where you really need it. There have been a few studies indicating that oral glucosamine supplements might help reduce the possible wrinkling, but not the hydration levels of your skin. Avoid the sun - that just seems obvious! - and use sunscreen to avoid further photo-damage.
Remember glycerin is your friend, as are the lower molecular weight hydrolyzed proteins, like silk or Phytokeratin, that penetrate your skin. Both of these ingredients will offer tons of moisturizing without oils.
When you are formulating mineral make-up for dry skin, make sure to include humectants like allantoin or silk powder to ensure you have a moisturizing ingredient, even in powdery formulas. Magnesium myristate treated sericite mica will offer moisturizing - it's a better choice than untreated sericite mica.
Join me tomorrow for more about skin types - the oily skin type!