In order for skincare products to work effectively they must penetrate the skin properly. To find out whether or not an ingredient does or does not penetrate the skin we should talk about:
A) The structure of the skin
B) The properties of skincare product which control skin penetration
A. The skin biology
The skin is made up of different cell layers designed in a brick and mortar pattern and each layer is a collection of:
1. Proteins
Keratin: which makes up the outermost layer of the skin. Keratin forms the rigidity of skin and helps with the barrier protection.
Collagen: long-chain amino acid which makes up the majority of protein found in the skin. Collagen is responsible for warding off wrinkles and fine lines.
Elastin: protein that forms elastic connective tissue, found in the dermis. Itโs responsible for giving structure to your skin. Lower levels of this protein cause your skin to wrinkle and sag.
2. Lipids
The mortar that helps lock in moisture and bind the cells together. Ceramidesย are a type of these lipids.
3. Peptides
Chains of amino acids that signal our cells to let them know how to function structurally, peptidesย are smaller thanย proteins.ย
4. Nucleic acids
These are the molecules that make up DNA.
The skin is composed of 3 main layers:
Epidermis
This is the outer layer of the skin which is responsible for protecting you from environmental damage. It does not contain anyย blood vessels so is dependent on the dermis for delivery of nutrients and waste disposal.ย The epidermis has 5 layers of its own:ย
1. Stratum Corneum:
This is the top layer of the epidermis. It consists dead cells that used to exist in the bottom layers.
Made of:
– Keratinocytes (Bricks)
– Epidermal lipid (Mortar): cells consist of Ceramides, fatty acids and lipids.
Main function:
– Preventing bacteria, viruses, and fungi from penetrating to deeper layers of skin
– Protection against abrasion and friction for the more delicate underlying layers.
– Preventing dehydration of the lower layers.
Skincare for this layer:
– Facial scrubs
– Cosmetic procedures like microdermabrasion
2. Stratum Lucidum
This thin layer of small cells that allows light to pass through it and is found only in the thick skin on the palms of your hands, and the soles of your feet.
3. Stratum Granulosum
Made of:
– lamellar granules: make up the bulk of the keratinocyte
Function:
“The granules of this layer contain lipids and break open to release their contents into the space between the cells in the stratum lucidum and stratum corneum layers. This bathes the stratum lucidum and the stratum corneum with important lipids that make up the skin barrier to prevent fluid loss.โ
Skincare for this layer:
Overuse of hydroxy acids, retinoids, and other exfoliating ingredients can damage this important layer.
4. Stratum Spinosum
Made of:
– Keratinocyte
– Desmosomes: interlock with each other and strengthen the bond between the cells prevent your skin from tearing and blistering.
– Langerhans cell: is a type of dendritic cell which functions by washes off bacteria, foreign particles, and damaged cells that occur in this layer.
Function:
In this layer the Keratinocyte cells change from cube to polygonal shape and start to synthesize Keratin.
5. Stratum Basale
The lower levels of the epidermis are where new skin cells are made.
Made of:
– keratinocytes: produce the protein known as keratin which is the main component of the epidermis. Keratin is what forms the rigidity of your skin and is why skin is waterproof.
– Melanocytes: responsible for producing the skin pigment, melanin.
– Merkel cells: function in the sensation of touch
Main function:
All of the keratinocytes are produced from this layer
responsible for making melanin which gives skin its color
Skincare for this layer:
This is where stem cells are located. Because this layer is the innermost layer, many topical products that you apply to the surface of your skin cannot reach this layer and have an effect. That is why applying stem cells to your skinโs surface is a waste of time โ the uppermost layers of the skin prevent large compounds like stem cells from reaching this deep layer
Dermis
The dermis comprises the thick, vascular layer of the skin lying beneath the epidermis. It’s function is to produce collagen and elastin and provide nutrients & blood supply to the epidermis. It is categorized into two different layers:
Reticular layer: is comprised of the strong connective tissue collagen
Papillary layer: contains nerves and capillaries
Dermis is made of:
– Fibroblasts: are the cells which synthesize collagen and elastin
– Collagen: is a long-chain amino acid making up 75% of the skin. It’s responsible for warding off wrinkles and fine lines. .
– Elastin: This protein is responsible for giving structure and support to the skin.
– Ground substance: which is gel-like made from glycosaminoglycans. Glycosaminoglycans are composed of hyaluronan, glycoproteins and proteoglycans. This substance is important in hydration and moisture levels in the skin.
– Nerves
– Blood vessels
– Hair follicles
– Sebaceous glands
Skincare for this layer:
Collagen injections and Retin-A creams help restore skin turgor by either introducing collagen externally or stimulating blood flow and repair of the dermis, respectively.
Hypodermis
This is the innermost layer of the skin composed mainly of fatty and connective tissue. It acts as a padding layer against shock and force trauma. It also works to reserve energy and maintain the body’s core internal temperature. Special connective tissue in the hypodermis connects the dermis to muscles and bones in the body.
Over the years various skincare products/ treatments have been developed to target different layers of the skin to help the skin repair itself and prevent aging. In order for these products/treatments to work they have to find their way in between these layers of brick and mortar to penetrate properly. So, will these products/treatments actually penetrate to be effective?
B. Properties that determine skin penetration
1. The physiochemical properties of the ingredient
Size of the molecules
Obviously the smaller the molecules in the ingredient, the easier the penetration would be! Typically only molecules of size 500 Daltons or less can effectively cross the skin barrier.
Example of the molecular weight of common skincare ingredients:
Water: 18 Dalton
Glycerin: 92.09 Dalton
Matrixyl: 578 Dalton
High molecular weight Hyaluronic Acid = 1.0 โ 1.5 Million Daltons
Ultra Low Molecular weight Hyaluronic Acid = 6000 Daltons
Lactic Acid: 90 Dalton
Glycolic Acid: 76 Daltons
Salicylic Acid: 138 Daltons
L Ascorbic Acid: 176 Dalton
Retinol: 286 Dalton
Retinal: 284.44 Dalton
Retinoic Acid: 300.44 Dalton
Phenoxyethanol (preservative): 138.16 Dalton
HA molecules are 3,000nm in diameter, whereas the intercellular space is only 15 to 50nm which makes it impossible for conventionally HA to penetrate into deep layers of the dermis. โScientists at Forlleโd Laboratories bioengineered HA molecules to a nano size (5nm) to cross the skin barrier deep into the dermal level.โ
Collagen has a very large molecule and can not penetrate the skin let alone reaching the dermis, where it is needed!! The reason that some people see good results using topical products which contain collagen is that the large molecule stays on the surface of the skin and prevent moisture loss, so the skin is kept hydrated and hydrated skin is plumper!dah!
Are molecules Oil-soluble or water-soluble
Oil soluble ingredients have the ability to slip through the bricks of the skin while water-soluble ingredients only work on the surface of the skin. This is the reason that we use Salicylic acid, which is oil-soluble to deep cleanse the pores and AHAs (Water-soluble) to exfoliate the surface.
The PH level
For example, โWhen the pH of a solution containing ascorbic acid is lower than a certain amount more of the ascorbic acid will be protonated and protonated ascorbic acid is neutrally charged which may allow it to enter the skin more easily.
The concentration of active ingredients
As an instance, “absorption of Ascorbic acid seemed to peak at 20%, the 25% ascorbic acid solution penetrated less than the 20%, and the 30% even less.โ
2. The ingredients delivery system
In order for products to penetrate the skin, different delivery systems are used:
Encapsulation: emulsifiers are used to encapsulate the ingredient and deliver it to the target layer. โThink of these as lubricants which penetrate deeper into the skin and bring whatever is encased in the micelle with it and helps both water-soluble and oil-soluble actives penetrate more deeply.โ Emulsifier examples: ethanol, PEGs, jojoba oil, propylene glycol. Nano-structured lipid carriers are the next-generation cosmetic delivery agents.
In-office treatments: Some procedures such as microneedling and laser treatments create small abrasions on the skin, which makes it possible for some skincare ingredients to penetrate the skin.
3. The time that is it going to stay on the skin
While leave on product, such as a moisturizers and serums, give the ingredients more time to penetrate, rinse off products rarely give ingredients enough time to penetrate.
4. The condition of the skin
The rate of penetration of skincare ingredients may increase four to 100 times when the skin is damaged!
In the next illustration I listed some common ingredients which have been proven to actually penetrate properly (if well-formulated) and the layer they should work on.
** Penetration means that the ingredient goes further into the layers of the skin, while absorption means that the ingredients make it all the way into your bloodstream.
