How Skincare Ingredients Work: From Barrier Function to Bioavailability

Why Understanding Ingredients Matters

There are many skincare ingredients in our products, that penetrate our skin barrier and deep into the layers. The ingredients in your skincare are found on the back of skincare packaging, in small print. It is often one of those things that goes unnoticed; it’s always the front of the packaging that attracts attention, containing the marketing buzzwords. The back is where the magic is; it contains the entire formulation, and if you understand it, you can work out which product is best for you. This is the INCI (International Nomenclature of Cosmetic Ingredients) list and will contain the active ingredients in the middle or at the end of the list.

Active ingredients are needed in small quantities to bring about change, targeting a specific concern. One of the main things you need to look out for is the active ingredients used to target your specific skin concern.

The most powerful skincare ingredients that have been proven to improve skin health:

1. Retinoids – Collagen-stimulating, increasing cell turnover
2. Niacinamide – Improves collagen and barrier function, reducing hyperpigmentation
3. Vitamin C – Reduces oxidative stress, brightening the skin
4. Alpha Hydroxy Acids (AHAs) – Remove surface dead skin cells

The efficacy of skincare ingredients depends on the complete formulation, including the size of the molecules and whether they are oil or water-soluble. The skin better absorbs smaller, oil-soluble molecules as our skin barrier is mainly made-up of lipids (oils). The efficacy can be further enhanced by combining ingredients that work synergistically.

Skin Structure 101: Where Do Ingredients Actually Go?

Our skin is made up of layers, the epidermis, dermis and hypodermis. Above the epidermis lies the stratum corneum barrier. Together, they work as a barrier against environmental damage and reduce water loss. The skincare ingredients we use penetrate different layers, so they should be chosen based on the skin layer/concern being treated.

The Epidermis

The epidermis is the top layer of the skin, and its main functions are:

• Protect bacteria and germs from entering the body
• Produces new skin cells to replace the dead skin cells
• Contains melanin, giving the skin its colour

The Stratum Corneum

This is the outer layer of the epidermis and the primary skin barrier, protecting against environmental factors and preventing water loss. It is made up of cells that are held by proteins and lipids, forming a “brick and mortar” structure. These are dead skin cells that are naturally shed every 4 weeks to give a fresher appearance. Exfoliating skincare ingredients can further enhance this process making it quicker to get smoother skin.

The stratum corneum is also where the acid mantle and microbiome are found. This is a slightly acidic, hydrolipid layer making up a protective ecosystem containing sweat, sebum and bacteria. A damaged stratum corneum can result in skin sensitivity and other allergies, such as acne and eczema.

The Dermis

The middle later, the dermis, makes up 90% of the skin, it contains:

• Collagen and elastin – proteins keeping the skin cells strong and flexible
• Hair follicles – for hair growth
• Sebum production – keeping skin soft and preventing too much water loss
• Sweat glands – regulating body temperature
• Nerves and blood vessels – keeping in touch with pain and temperature changes, and providing the skin with nutrients.

The products we apply to our skin need to penetrate through the layers. Poorly formulated products can mean that most of the ingredients never get past the epidermis. Active ingredients need to be smaller, lipid-soluble molecules to penetrate the dermis layer. Certain ingredients in the formulation can further enhance penetration to deeper layers, such as urea or jojoba plant oil. The method we use to apply the product can also further enhance penetration. This includes applying products to damp skin or using spicules, allowing active skincare ingredients to be delivered where the skin issues originate.

Barrier Function: The Foundation of Effective Skincare

A strong skin barrier will protect us against bacteria, UV rays and water loss. When the skin barrier becomes compromised, our skin can become dry and develop psoriasis or dermatitis.

Over time, different factors can weaken the barrier:

• Climate – too dry or humid
• Sun damage – especially where adequate spf not used
• Over exfoliation – trying to keep the skin too clean
• Soaps or detergents – can change the pH of our skin affecting the acid mantle
• Stress – our mental health can show up on our skin
• Genetic factors – increase the likelihood of certain conditions, such as psoriasis

When the skin barrier becomes compromised, skin symptoms and conditions can develop. These can include itchy, dry and scaly skin. Acne, pimples, sensitive and inflamed skin. Rough or discoloured patches on the skin. Bacterial or fungal skin infections. It also makes it difficult for skincare ingredients to properly penetrate the skin barrier.

Transepidermal Water Loss (TEWL) can be used to measure the health of the skin barrier. A low TEWL suggests that the skin is losing very little water from its surface, indicating a healthy skin barrier. Choosing the right skincare products can help reduce TEWL. We can use skincare ingredients like humectants, such as glycerin, urea and hyaluronic acid. The skin barrier is held together by lipids; including ceramides, cholesterol and fatty acids. These are excellent skincare ingredients that help stabilise the skin structure, lower the skin pH and reduce TEWL.

Read here to find out more about products that can further help keep our skin barrier healthy.

Penetration vs. Absorption: What’s the Difference?

The words penetration and absorption are used to talk about skincare, but they actually mean very different things. Penetration is where skincare ingredients pass through the skin barrier and into the deeper levels of the epidermis. Absorption is where skincare ingredients pass through the skin’s barrier, all the way through the epidermis and dermis, all the way into the bloodstream, entering systemic circulation.

We are often told to avoid using certain products because it contains ‘chemicals’ that can be absorbed into the bloodstream. This is not true; most skincare products are topically applied, and the ingredients used stay within the upper layers of the skin, you can read more about this here. The formulation of the product determines how well it penetrates through the skin barrier.

Bioavailability: Why Formulation is Everything

Bioavailability refers to how long and how efficiently active skincare ingredients take to penetrate the skin barrier and reach their target. The bioavailability depends on a number of factors discussed below:

Molecular Size & Solubility

Active skincare ingredients with a low molecular weight that are lipophilic (lipid-loving) are able to penetrate the skin barrier more easily. An example of this is retinol, its smaller size and ability to move through the lipid layers of the skin cells.

Active skincare ingredients with a higher molecular weight that are hydrophilic (water-loving) are not able to penetrate as easily through the skin barrier. The formula needs a special delivery system to help it penetrate the skin barrier more efficiently. An example of this is hyaluronic acid, which is a much larger molecule and, in its normal state, will sit at the top of the skin surface, forming a thin film, helping the skin lock in moisture. To make it penetrate deeper, it can be broken down to a smaller size and formulated with lipids to allow them to travel deeper.

pH Dependancy

Some skincare ingredients work better at a lower, more acidic pH. This includes vitamin C (L-ascorbic acid) and exfoliating acids (AHAs and BHAs).

Using products with the wrong pH can make actives less effective, disrupt the skin barrier, and increase skin sensitivity.

The skin barrier has a lower pH due to its acid mantle, and using more alkaline ingredients (found in a lot of soaps) will disrupt this, causing skin irritations.

Using skincare with a lower, more acidic pH allows the actives to penetrate the skin barrier easily, improving overall barrier health.

Stability and Oxidation

Some skincare ingredients are unstable and need specialised formulation and packaging to help prevent degradation and prolong their shelf life. Some of the factors that need to be considered:

• Air or oxygen exposure can degrade actives in products causing discolouration
• High temperatures can speed up the oxidation of actives
• UV rays in light can cause disruption in delicate ingredients
• pH levels must be stable for preservatives in the formulation to work effectively

Vitamin C (L-Ascorbic acid) can degrade very quickly, changing from a clear solution to a brown discolouration. It is stabilised using opaque, airless packaging, the formulation is of low pH and often includes Vitamin E and Ferulic acid.

Retinols can also degrade in the presence of air and light and need to be stored in opaque packaging and formulated with antioxidants.

Plant-based oils are also prone to becoming rancid and degrading in the presence of light, air and higher temperatures. They also need to be formulated using other skincare ingredients such as antioxidants like Vitamin E and stored in opaque packaging.

Delivery Systems

A specialised delivery system can be used to transport active skincare ingredients that are more fragile to target areas in the skin. These are formulations or technologies that enhance penetration and stability.

Some key components to delivery systems:

• Encapsulation – liposomes or capsules enclose active skincare ingredients and carry it to the targeted area. Making sure that the active remains stable and potent.
• Time-release: this is when active skincare ingredients are released over time. For example, microemulsions contain actives within oil-in-water or water-in-oil droplets, controlling their release into the skin barrier. This can be used to hydrate for longer or to gently exfoliate for longer.

Ingredient Categories & How They Work

Skincare ingredients can be put into different categories depending on their purpose and how they work within the skincare formulation.

Actives

• Retinoids – speed up cell turnover, enhancing exfoliation and controlling acne, reducing inflammation, redness and managing pigmentation. Increases collagen production, improving skin texture and elasticity, reducing fine lines.
• Vitamin C – a powerful antioxidant neutralising free radicals from pollution and UV radiation, preventing cellular damage. Boosts collagen production, brightens skin tone and controls pigmentation by inhibiting the enzyme tyrosinase. Strengthens the skin barrier to prevent moisture loss.
• Peptides – amino acid chains that signal cells to produce more collagen; act as carriers carrying trace elements, helping with barrier repair. By inhibiting enzymes, they slow down the breakdown of collagen and elastin.

Exfoliants

• AHAs – Breakdown of bonds between dead skin cells, exfoliating the skin surface, giving a smoother texture. This unclogs pores, preventing acne breakouts, increasing cell turnover and fading discolouration caused by sun damage. AHAs are water-soluble and can also act as humectants, attracting moisture and keeping the skin hydrated.
• BHAs – Penetrate deeper than AHAs as they are oil-soluble, clear clogged pores, reducing and preventing acne and blackheads. Can reduce the appearance of fine lines and wrinkles, improving overall skin texture.
• PHAs – Improve skin texture and brightness by exfoliating dead skin cells. These are gentle exfoliants that work at the surface level and are best used with other actives. They have humectant properties and fight free radical damage. Ideal for strengthening the skin barrier and reducing inflammation, so suitable for the most sensitive skin.

Barrier Support

• Ceramides – These are lipids that hold skin cells in the protective skin barrier, keeping moisture in and preventing environmental damage. Reducing skin irritation, dryness and eczema.
• Niacinamide – Strengthens the skin barrier, regulates sebum, brightens skin tone and improves texture by reducing inflammation.
• Panthenol – Deeply hydrating, repairing the skin barrier and acts as an emollient to soothe inflammation and regenerate the skin.

Hydration System

• Humectants – Draw moisture from the air (in humid weather) or from the deeper layer of the dermis to the epidermis. Works best when applied to damp skin and combined with an occlusive to seal in the water. Some popular humectant ingredients include: hyaluronic acid, glycerin, urea and panthenol.
• Emollients – Form an oily layer on the surface of the skin, trapping water. Repairs the skin barrier by filling any gaps and softens rough, flaky skin, making the skin smoother. Emollients have different oil-to-water ratios so you can choose between ointments, creams and lotions. You can read more about this here.
• Occlusives – Seal in moisture, preventing TEWL by creating a physical barrier on the skin surface. They heal dry and damaged skin. Some of the most commonly used skincare ingredients are mineral oil, petrolatum, dimethicone, beeswax, cocoa butter, and jojoba oil.

Factors That Influence Ingredient Performance

Good skincare products are designed with skincare ingredients that address specific skin concerns. However, despite that, many factors can affect the performance of the products being used:

• Product Formulation
  • Size of molecules, small penetrates deeper into the epidermis, and larger stays at the surface
  • Oil and water-soluble ingredients, oil-soluble (lipophilic) can penetrate the lipid rich skin barrier more effectively than water soluble ingredients
  • pH levels affect the efficacy of active ingredients; a lower acidic pH helps maintain the skin barrier and acid mantle
  • Higher concentrations of active ingredients may be more effective, however can irritate the skin
  • Stability ingredients or penetration enhancers help active ingredients get through the skin barrier and have a timed release.
• Skin Condition
  • If the skin barrier is compromised, it can prevent actives from penetrating properly, or become irritated with concentrated skincare ingredients
  • Skin cell turnover reduces dramatically as skin ages so more exfoliation is needed and it will take longer to see results
  • Higher water levels in the skin help skin ingredients to penetrate better
  • Skin type and skin concerns, determine the type of formulations and ingredients that are most suitable
• Application
  • Applying the thinnest product and layering it with thicker products allows better penetration of skincare ingredients
  • Higher moisture levels in the skin allow better penetration
  • Exfoliation of dead skin cells lets the active skincare ingredients pass through the skin barrier more effectively
  • Warmer skin makes the skin more permeable to the products the will allow and skin temperature
• Lifestyle
  • UV Radiation from increased sun exposure can damage the skin barrier, break down collagen and cause photoaging
  • Harsh climates and pollution can affect how products function and blend with the skin
  • Chronic stress, smoking and a poor diet can contribute to skin inflammation and slow down skin repair reducing the efficacy of products
• Biology
  • As we get older, our skin becomes thinner, collagen, oil production and cell turnover are reduced, we need more concentrated actives formulated with deeply nourishing skincare ingredients
  • Our hormones change during different periods of our life, including puberty, pregnancy, menopause and also during times of stress. All of this affects our skin sebum production and sensitivity
  • Individual genetics determine our skin type and barrier strength

Myths About Skincare

Despite the scientific evidence, there are misconceptions about skincare and the potential harm skincare ingredients can cause. These are misunderstandings of research and opinions of what works.

Here are five common skincare myths:

1. Natural and chemical-free products are better – there is no such thing as chemical-free, and no clear definition of what ‘natural’ is; this doesn’t really mean anything and is just marketing
2. A lot of skincare products are needed to build a good routine – the right products mean a simple combination can work well
3. You can shrink your pores – by using cleansing products, it is possible to reduce the appearance of pores, but the size of the pores are genetically determined
4. Makeup will make you age faster – skin must be hydrated and prepped before applying makeup, the skin needs to be cleansed thoroughly after removing it all
5. SPF is only needed in sunny weather – SPF protects the skin from UVA and UVB rays

How to Choose Ingredients That Actually Work

Before choosing the right skincare ingredients, determine the skin type, along with skin concerns and future goals. Look for evidence-based skincare ingredients near the top of the ingredients list. This is to ensure the active skincare ingredient is concentrated enough. When using products that are highly concentrated, they must be started slowly to avoid the skin barrier becoming irritated.

Some key skincare ingredients by skin type and concern are:

• Aging – Retinoids, Vitamin C, Peptides
• Dry or Dehydrated – Glycerin, Hyaluronic acid, Ceramides
• Oil – Glycolic acid (AHA), Salicylic acid (BHA), Niacinamide
• Sensitive – Panthenol, Aloe Vera

Once you have identified your skin concerns, choose the right ingredients and add them to your routine. Skincare ingredients can also be combined to enhance results, for example, using exfoliants like AHAs to remove dead skin cells before applying ceramides, or using hyaluronic acid before applying retinol to increase penetration into the skin barrier.

Skincare is Chemistry + Biology

The product is chemistry; it contains a cocktail of active skincare ingredients formulated with other skincare ingredients, helping them work better by managing pH and molecular weight.

Your skin is biology. This includes the structure, how it connects with the rest of the body and manages the ecosystem on the surface of the skin.

True skincare is when your skin’s biology interacts with the chemical formulation in your skincare product.