Skin Penetration

  • By 1thuybradceuticalsadmin
  • April 4, 2022
  • Education

We are often asked by customers if growth factors get into the skin and whether you need a delivery system in order for a product to be effective.

In order to better answer that, we’ve put together this post on skin penetration and the different routes that skincare ingredients can get into the skin.

If you haven’t already, give our post on growth factors a read as well.

Skin Anatomy

In order to understand how ingredients make their way into the skin, it’s important to have a basic understanding of skin anatomy and function.

skin anatomy

As you can see in the visual above, the skin is divided into the main parts: the epidermis and the dermis.

The epidermis is the skin you can see and is made up of the stratum corneum (the dead but still biologically active skin cells that form the skin barrier) and the living epidermis underneath.

Meanwhile, the dermis is made up of papillary and reticular regions. Because this tissue is vascular, the dermis is water-rich and also rehydrated and supplies nutrients via circulation.

It’s the stratum corneum though that is most important in regards to penetration of ingredients. Also known as the skin barrier, it’s designed to keep things out.

The Epidermal Barrier

skin barrier model

The brick and mortar skin model is a common analogy used to explain the structure and function of the skin barrier. The “bricks” are skin cells called corneocytes and the mortar between them is the lipids.

Corneodesmosomes are adhesion structures that attach the corneocytes together and their degradation is believed to start desquamation (your skin’s natural exfoliation process where dead skin cells slough off). Within the corneocytes, you’ll find intracellular humectants (the Natural Moisturizing Factor) that help attract moisture from our environment. The intercellular lipids are mainly composed of ceramides, cholesterol, and fatty acids.

Penetration Routes

penetration routes

The most common way that ingredients pass into the skin is through the intercellular route (also sometimes referred to as the transcellular route), meaning the ingredients pass through the skin cells that make up the skin barrier. This route is well suited to hydrophilic (think water loving) and polar molecules provided they’re smaller than 500 Daltons.

If an ingredient is lipophilic (oil loving), it can take the intracellular route – meaning it passes through the tight lipid junctions between the skin cells. Sweat glands and hair follicles, while less studied, offer an alternative called the transfollicular route.

As you can see in the visual, we also have various methods of enhancing penetration of active ingredients. Mechanical delivery, like via microneedles, is just one example.

Enhancing Penetration

As we discussed in our posts on layering skincare, not all ingredients require help getting into the skin and some may even work best superficially. It’s important to be discerning in our approach.

Once you’ve decided on an ingredient that you wish to help get into the skin, it’s important to understand how the structure and size of the molecule will determine what path it takes into the skin and which method is best in helping it along.

You’ll also want to be aware of what factors influence the permeability of the skin and penetration rate. More hydrated skin is more permeable since corneocytes swell – which is why occlusion can be used to better penetration. Heat can also influence penetration by influencing the kinetic energy.

When it comes to methods of getting active principles into the skin, we have passive and active methods.

Passive Penetration Enhancement

Using passive methods largely involves using chemical penetration enhancers as well as adjusting the formulation to better get into the skin.

Some common penetration enhancers include:

  • urea
  • alcohol
  • glycerol
  • fatty acids like oleic acid
  • surfectants
  • glycols
  • esters
  • terpenes

Each penetration enhancer will work differently. Oleic acid and surfactants, for example, work by temporarily alternating the skin barrier. Urea and its derivatives improve penetr

Examples of penetration through formulation:

  • oil in water emulsions
  • vesicular systems like liposomes
  • non-vesicular systems like solid lipid nanoparticles

An emulsion just means that you have a water phase and an oil phase that you’ve combined together and then added an emulsifier to keep the two phases suspended. Oil-in-water (O/W) emulsions are when oil is the internal phase and this type really penetrates the stratum corneum well.

Liposomes are the most common type of vesicle and the most studied. We won’t go into all the different variations and types in order to keep things from getting too confusing and will instead use liposomes as our example.

vesiculars systems

Typically made of phospholipids, liposomes are vesicles where the stacked phospholipids create a hydrophilic barrier lining both the outside and the inside. The space in the middle is an aqueous compartment where hydrophilic actives can be placed where any hydrophobic ingredients would be placed where the tails meet.

Solid lipid nanoparticles, which have a lipid core, are an example of a non-vesicular system. Biphasic formulations and micelles are a few more examples.

Active Penetration Enhancement

While passive penetration involves chemical penetration enhancers as well as carriers to aid penetration of ingredients, active penetration means using physical methods.


A pulsed, high voltage current is used to make temporary pathways in the skin barrier for hydrophilic ingredients.


A very small electrical current is used to transport charges molecules into the skin.


Ultrasound is used to alter the skin barrier as well as increase skin temperature increases permeation of ingredients into the skin.


Microneedles are used to create temporary channels into the skin. Depth and closure time depends on needle length.

Bradceuticals and Growth Factors

Hopefully this post was informative and you learned something new about skincare. To finish this up, we want to come back around to the topic of Bradceuticals products and the penetration of growth factors.

As we discussed in our post on layering, growth factors are large, water soluble molecules and likely don’t penetrate intracellularly. And yet studies show that applied topically, they work for skin rejuvenation. Why is that?

It’s believed that topical growth factors may penetrate via the hair follicles while other sources believe that even if they don’t penetrate, they can still communicate with cells. The bottom line though is that the research shows they work without a delivery system.

We choose not to include vesicular delivery systems because first and foremost, they haven’t been shown to be necessary. Omitting them and instead using penetration enhancers like glycerol and urea (which work by supporting the skin barrier rather than altering structure) allows us to offer high quality stem cell conditioned media serums that don’t break the bank.

And lastly, liposomes and other delivery systems aren’t very proven yet. Some studies show that they don’t actually penetrate past the skin barrier. So instead we choose to keep prices reasonable and instead educate customers on more proven physical penetration methods like microneedling if they’re interested.

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