Understanding the scientific bases of skin care can better inform personalised skin care. Photo credit: Content Pixie on Unsplash.
Skin care is often viewed as superficial rather than scientific. But understanding the chemistry behind formulations can help you refine your routine. From being able to understand the ingredient lists to knowing what order gives the most effective outcome, after this you’ll be one step closer to achieving your dream skin.
From being able to understand the ingredient lists to knowing what order gives the most effective outcome, after this you’ll be one step closer to achieving your dream skin.
Skin care as systems
There are two main types of skincare systems: oil-in-water (O/W), where tiny oil droplets are suspended in a continuous water phase, and vice versa, water-in-oil (W/O).
A common question in skin care is why aren’t products just made of active ingredients—those compounds included to directly target skin concerns? The answer lies in viewing skin care products as systems rather than ingredients. There are two main types of skincare systems: oil-in-water (O/W), where tiny oil droplets are suspended in a continuous water phase, and vice versa, water-in-oil (W/O). Although water and oil are famously immiscible, this can be overcome by using emulsifiers—molecules containing both a hydrophilic part (attracted to water) and a lipophilic part (attracted to oil). Beyond forming stable emulsions, some ingredients enhance the efficacy of active compounds. For example, penetration enhancers and solubilisers, which work by disrupting lipid bonds, reducing the resistance in the stratum corneum (the outermost barrier of the epidermis). Other ingredients, such as silicones (e.g. dimethicone), shea butter, and coco-caprylate, are included to improve the sensory experience, while preservatives extend shelf life.
Cleansers
Cleansing first may seem obvious as, if you were to do it at any other point, it would wash away the previous products.
Many of us follow the same order of skin care products every time without realising why. Cleanser, followed by intermediates, then moisturiser and finally SPF. Cleansing first may seem obvious as, if you were to do it at any other point, it would wash away the previous products. Whilst this is true, cleansing also removes any oil or dirt that would prevent other products being absorbed as effectively. As a result, double cleansing, using an oil-based cleanser followed by a water-based cleanser is strongly recommended. Oil-based cleansers help break down and remove oil-based impurities such as makeup or suncream and, similarly, water-based cleansers remove water-based impurities such as sweat and environmental pollutants and work better once the oil-based impurities have been removed. It may also seem intuitive that thinner products should be applied first and thicker products last. This is because thicker products prevent effective penetration of thinner ones by forming an occlusive barrier. This is a protective layer on the skin which physically seals in water and protects against external irritants, whilst simultaneously blocking more dense ingredients passing through.
So, we’ve established that cleansers remove dirt and oil but how do they do this? In order to clean the skin, water needs to be able to reach the surface, which is usually prevented by surface tension, so we include surfactants, such as sodium cocoyl isethionate. Surfactants have the same general structure as emulsifiers, allowing them to orient in a sphere with the lipophilic ends facing towards each other, forming a micelle. Dirt and sebum on the skin are attracted to the environment the micelle creates to avoid water interactions and are then easily rinsed away with the water.
In order to clean the skin, water needs to be able to reach the surface, which is usually prevented by surface tension, so we include surfactants, such as sodium cocoyl isethionate.
Surfactants vary with charge, and it’s important to use one that matches your skin type. Anionic (negatively charged) surfactants usually contain sulphates such as sodium lauryl sulphate. These are harsh surfactants which strip away natural oils from the skin and so are best used on oily skin or to remove makeup or sunscreen. Amphoteric surfactants such as cocamidopropyl betaine can be positively or negatively charged based on the pH of the solution and so are slightly gentler, making them ideal for a wide range of skin types. Non-ionic surfactants including decyl glucoside and glycereth-2 cocoate are the gentlest, so are better for sensitive skin. Often a combination is used to maximise efficacy and reduce irritation.
Active ingredients can also be found in cleansers, usually at a higher concentration as they can provide benefits despite short contact time. Some active ingredients such as retinol and vitamin C need a lot of time to absorb so aren’t as effective in cleansers and so BHAs (e.g. salicylic acid), AHAs (such as glycolic acid), and PHAs are better options.
Intermediates
Serums and toners are typically lightweight O/W emulsions, allowing them to penetrate deep into the skin, maximising delivery. If you have any skin concerns, now is the time to treat them by choosing products containing active ingredients that suit your skin.
Vitamin C acts as an antioxidant by neutralising free radicals (highly reactive molecules with unpaired electrons) generated in the skin by UV exposure and environmental stressors such as air pollution, while also helping to brighten and even skin tone.
Hyaluronic acid is a humectant which means it draws water from the air and the dermis (the middle layer of your skin), creating a moisture barrier which keeps the skin hydrated.
Peptides are amino acid compounds which stimulate the production of collagen to repair damaged skin, improve skin elasticity, and promote anti-ageing effects. They are a good alternative to including larger collagen proteins in the formula as these struggle to be absorbed into the skin fully whereas smaller peptides penetrate more easily.
Vitamin A has many forms such as retinoids, retinal, and retinol. They all encourage the production of new skin cells in the epidermis (the upper layer of your skin) by binding to receptors and can also help to reduce acne.
Ceramides are lipids that help to maintain the skin’s barrier function by filling the area between cells, limiting penetration of microbes, and preventing moisture loss meaning they are good for dry, sensitive skin.
However, whilst all these effects sound appealing, layering too many actives can damage the skin barrier and lead to irritation. Certain actives are also ineffective when used together—for example, benzoyl peroxide can deactivate vitamin A, while vitamin C and retinol require different pHs so disrupt each other’s effectiveness.
Moisturiser
It is a good idea to use a moisturiser next as they protect the skin and trap in the products underneath by using a combination of occlusives, humectants, and emollients. Occlusives, such as waxes and fatty acids, have a heavier, thicker consistency, creating a barrier over the skin. However, as occlusives tend to be quite oily, they are best for dry damaged skin, whereas those with acne-prone skin should opt for non-comedogenic moisturisers, to prevent clogged pores. Emollients such as butters, lipids, and squalene prevent water loss by forming a layer on the skin’s surface and filling the gaps between dead skin cells. Combining these ingredients creates a synergistic effect of humectants attracting water into the skin and occlusives locking the water in.
SPF
The long-term results of all the above steps are very limited if they are working against UV damage due to lack of SPF. UVA (longer wavelength UV) rays can penetrate deep into the skin through the dermis, leading to photoaging and indirect DNA damage. UVB (shorter wavelength UV) rays can affect the epidermis causing sunburn and direct DNA damage. Suncreams contain a mixture of UV filters which each offer different protection across the range of wavelengths. There are two types of suncream: chemical suncreams which work by absorbing and dissipating the energy of the radiation and physical suncreams which reflect UV as well as absorbing it (creating a white cast), often made of minerals such as zinc oxide.
…whilst it’s tempting to try new products you see on social media, for the best results it’s important to resist always jumping on new trends.
The phrase ‘consistency is key’ manifests itself heavily in skin care, and whilst it’s tempting to try new products you see on social media, for the best results it’s important to resist always jumping on new trends. Skin cell production occurs at the base of the epidermis, and the cells move up to the surface of the skin before breaking off. This cycle takes around 28 days which is why it is often advised to wait a minimum of 28 days before assessing the effect of a new skin care product. It is important to do your research before buying products as misinformation is rampant on social media, so make sure your science is sound before making your next purchase.
