When it comes to understanding the hows and whys of skin care, it all comes back to molecules. With skin care becoming more scientific, in everything from its formulation to its advertising, it’s easy for anyone who isn’t a self-proclaimed ‘skintellectual’ to feel confused. If you have always wondered how your favourite cream or serum works, or what terms like ‘time-release delivery system’ and ‘low molecular weight’ actually mean, you’ve come to the right place.
Let’s Get Deep
Before you can understand how a product does or doesn’t penetrate the skin, we need to revisit some basics. The skin is made up of three primary layers – the epidermis, the dermis and the hypodermis or subcutaneous layer – which not only protect our inner organs from harm and bacteria but keep us waterproof and looking, well, human. Within the top layer of the skin (the epidermis, keep up!) there are four or five sub-layers, including the stratum corneum and the stratum basale. In short, that’s a long journey for any ingredient to go on in order to reach the dermis, where key proteins like collagen and elastin reside, hence why few ingredients actually make it. Most will stay on the surface or will penetrate down to the lower layers of the epidermis, where changes to the skin’s health can still be made.
In order for an ingredient to reach these lower layers, it needs to first pass through the epidermal barrier or lipid layer. While this barrier is predominantly the first line of defence against the environment, it isn’t completely impenetrable. The top layer is made up of tightly packed cells cemented together by lipids, so for an ingredient to pass through this top layer it needs to either be absorbed by the skin cells or to find a way through the small lipid gaps between the cells, which is where molecule size comes into play.
The smaller the molecule, the easier it will penetrate the surface of the skin. Small molecules or those with a low molecular weight can squeeze through any gaps in this lipid glue while larger molecules remain at the surface, either being slowly absorbed by the cells or sitting on top. For scientists, the ideal weight of a molecule that can penetrate the skin is around 500 Daltons (Daltons are a unit of measurement used to determine the mass of a molecule or atom). Most experts say that ingredients with a molecular weight greater than this can’t penetrate the skin’s lipid layer and therefore can go no further than the stratum corneum. This is fine for rich moisturisers that are designed to combat surface dryness and prevent moisture loss, but it’s not so good for antioxidant serums that need to go deeper.
It’s also easier for oil-soluble molecules to penetrate the skin compared to water-soluble ones, due to the skin’s outermost lipid layer. For example, Salicylic Acid is oil-soluble, which is why it can successfully penetrate into the pores, but an AHA like Lactic Acid is not and so does the majority of its work at the surface. But, scientists have found a way around this.
To ensure ingredients that are unstable or too large in molecular structure can reach the lower layers, scientists use micro-encapsulation to aid their delivery to the layer of the skin that can utilise them most effectively. Encapsulation involves encasing a molecule within a lipid sphere or bubble, to protect the fragile molecule hidden inside from damage and from being broken down too early, while also simplifying its path into the skin. These protective bubbles can be both synthetic and natural in composition, such as Jojoba Oil, and can significantly improve the potency of topical ingredients. This is why the technique is so popular when it comes to antioxidant serums: the lipid bubble protects a volatile ingredient like Vitamin C from being broken down to ensure your skin reaps more of its benefits.
Encapsulation can also be used to make intensive ingredients more tolerable for the skin by using time-release technology. By releasing an active ingredient like Retinol slowly into the skin, there is less chance of a severe reaction taking place, something the scientists at Medik8 keep in mind when developing any Vitamin A product. “Retinol is not without its problems and can often cause irritation. Because of this, we’ve included time-release technology (in all Medik8 Retinol products) which essentially drip feeds Retinol into the skin slowly overnight, thereby reducing the risk of irritation,” explains Formulation & Development Director Daniel Isaacs. “Our Crystal Retinal products have a patented time-release delivery system that encapsulates the ingredient Retinaldehyde in a crystal molecular vehicle that is broken down by the skin’s natural enzymes upon contact. This unique action controls the release of the active to ensure the formula remains stable, absorption is optimised and the highly-potent formula is distributed evenly and constantly throughout the night.”
Sounds amazing, right? But not every ingredient needs to be encapsulated to work. AHAs, essential oils, peptides and low molecular weight Hyaluronic Acid can all transform the skin without using encapsulation methods, while some products work their best at the surface. Products like sunscreens, healing balms and cleansers that, by design, are washed off before any active ingredients have time to penetrate the surface, are all beneficial despite their inability to reach the lower layers of the skin. For all-round skin health, try to include a mix of products that address your biggest complexion concerns at and below the surface.
National Center for Biotechnology Information (NCBI)