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The stratum corneum is the outermost layer of the epidermis. As the skin’s primary defense, it has to keep bad things out. That doesn’t mean that it is impermeable, but some molecules will have a frustrating time trying to penetrate it. Increasingly, skin care formulas are being manufactured to ensure that they penetrate and interact with the stratum corneum. It is this interaction that is the current buzz in skin care.
So let’s take a look at the stratum corneum, how our anti-aging actives can penetrate it, how to protect it and – drum roll – how to go beyond it.
Stratum corneum means 'horny layer' in Latin and it consists of a lot of dead cells (corneocytes). Cells of the stratum corneum contain a dense network of keratin, a protein that helps keep the skin hydrated by preventing water evaporation. They also absorb water.
It is important to know that this layer is responsible for the "spring back" or stretchy properties of skin. A weak, glutinous protein bond pulls the skin back to its natural shape. This is why it is vital to ensure your regimen includes corneotherapy – the recovery of the stratum corneum.
Given that the main purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress, it also means that getting good things through the barrier can be tough. The challenge for cosmetics manufacturers is to develop a formula that enables an ingredient to penetrate the SC. And then it has to stay there.
This means that most formulas include penetration enhancers. Ever wondered why alcohol turns up so much in cosmetics? Well, it is one of the more common penetration enhancers. Propylene glycol is another ingredient that you’ll notice in many formulas because it is a solvent and penetrates the skin acting as a carrier for other ingredients. Others that might look familiar are oleic acid and isopropyl myristate.
Some skin care formulas use specially developed penetration enhancers to deliver ingredients like vitamin C or retinol. For example, BRAD uses an encapsulated retinol in its Sublime Youth Creator Gel-Cream ($245 in the shop), as does Amarte Eyeconic Eye Cream.
Liposomes work in a number of different ways, but basically they are thought to be useful for penetrating the SC and delivering actives en route. So you may see that an ingredient is liposome encapsulated. E'shee Clinical Esthetic Vitalizing C Serum ($119) has liposome vitamin C. Update: Community member, Kathy, alerted me to some Danish research that claims to demonstrate the liposomes don't penetrate the skin, but are "highly compromised by the skin barrier" (source).
Even more high tech is LiftLab Lift + Perfect ($250) with a copper heptapeptide-14 panthotenate in a special delivery capsule that has an affinity with the FGF fibroblast where it can target the matrix proteins, elastin and collagen. Skin Nutrition claims that the active ingredients in Cell CPR ($150) are “delivered intelligently with proprietary multi-encapsulation and delivery technologies.” Meanwhile, Nutra-Lift’s Rejuvenating A Nano Renue ($48) has nano gold particles that act as the delivery system for a peptide that is supposed to have an impact on collagen production.
A discussion of some of these delivery systems is in a book called Cosmetic Dermatology: Products and Procedures, and I was excited to discover that ultrasound is highlighted as a device for penetration enhancement. During an ultrasound treatment, the skin is exposed to energy that alters the skin barrier and can enhance the diffusion of topically applied actives. Furthermore, ultrasound doesn’t stop at the SC. The waves also help diffuse the active ingredients at the cellular level where they oscillate the cells at high speed. This changes the cell membrane (the author speculates that the membrane may be disrupted) and, as a result, the cells are more receptive to the ingredients. Ultrasound is the key technology used in our device, the Truth Vitality Lux Renew ($279 in the shop).