IS SKIN LIKE A SPONGE?
Very often, the effectiveness of a cosmetic is taken for granted: according to common thinking, the active ingredients contained within creams, gels, serums and other cosmetics are absorbed immediately by the skin.
In reality, the skin does not behave like a sponge (as is often implied by various advertising slogans)!
If your skin were a sponge…
...we could say goodbye to aesthetic medicine forever and we could show off young, beautiful, glowing and wrinkle-free skin for eternity.
Unfortunately, this desirable ambition is not easily achieved through the simple application of a cosmetic to the skin.
Formulation difficulties
One of the major difficulties in formulating a cosmetic concerns the skin absorption of cosmetics: in fact, the skin is the most effective protection system of our body, whose main function is to hinder the entry of certain substances , not to encourage it.
Despite acting as a protective shield, the skin is not completely waterproof, because it is able to absorb - at least in part - some substances with which it comes into contact.
When formulating a cosmetic, it is important to know the structure and functions of the skin, and to implement some useful strategies to promote the absorption of the active ingredients contained within it.
Absorption of Cosmetics: the "Problem" of the Skin Barrier
Since the skin is structured to hinder the passage of substances foreign to its own physiology, it is therefore clear that this factor must be considered when formulating a cosmetic product, the objective of which is instead to allow the active ingredients to penetrate through the skin.
Functions of the Skin
The skin is an extremely complex organ, used to perform essential functions for our survival.
To understand how the active substances of cosmetics can be absorbed through the skin, it is essential to study some functions of the skin, in particular:
- Barrier function;
- Defense function against infections;
- UV protection function.
The stratum corneum is the outermost layer of the skin, made up of flattened, dead cells similar to scales, rich in keratin.
The cells are "cemented" - that is, joined - by a viscous layer made up of a mixture of fats.
The particular composition of the stratum corneum gives the skin its protective function: in fact, the skin represents the body's most effective system of isolation from the external environment, preventing the entry of allergens, pathogens and other potentially dangerous substances.
Infection Defense Function
In the most superficial layer of the skin (called the stratum spinosum-granulosa of the epidermis), there are some cells known as "Langerhans cells".
These special cells are essential for:
- intercept possible allergens or pathogens;
- activate local immune defenses.
When the defensive activity of the Langerhans cells is lost, the skin is more exposed to the risk of infections; therefore, it is a good idea to apply protective cosmetics to the skin, capable of protecting these cells.
In this sense, cosmetics will have to guarantee the skin absorption of the active molecules present in the formula, in order to protect - in this case - the Langerhans cells.
UV Protection Function
The skin performs another important protective function against UV rays: when not filtered adequately, ultraviolet rays can cause damage of varying degrees in terms of:
- skin cells;
- DNA;
- dermo-connective matrix.
In case of sun exposure, UV rays can reduce the activity of Langerhans cells: in this case, it is important to ensure adequate sun protection for the skin by applying cosmetics with anti-UV filters.
How to Penetrate the Skin Barrier?
We have seen that one of the main factors to evaluate when formulating a cosmetic is overcoming the skin barrier.
It has been observed that some cosmetic substances tend to flow more easily through the skin barrier because they are more compatible with the skin.
In general, a cosmetic substance is more likely to be easily absorbed by the skin when:
- it is similar to the lipid component of the skin, i.e. it is fat-soluble: it is no coincidence that oil-soluble substances (e.g. vitamin A, E, D etc.) tend to be absorbed more easily by the skin;
- it has a low molecular weight: small substances (less than 500 daltons) tend to flow easily through the skin barrier;
- it is fluid at room temperature;
- has a low boiling point;
- it has a simple molecular structure: "bulky" molecules, structured with double and triple bonds, struggle to pass the skin barrier compared to molecules with a simpler structure.
How to deal with water-soluble and large molecules?
Substances similar to water (water-soluble) and those with a high molecular weight (i.e. large) struggle to penetrate the skin barrier.
In fact, "heavy" molecules such as hyaluronic acid and collagen can be absorbed inconsistently or partially, often remaining anchored to the corneal keratins (the proteins present on the skin, which constitute the stratum corneum of the epidermis).
