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The Biochemistry of Skincare

We’ve all seen the craze surrounding skincare routines in the past few years, particularly with YouTubers and celebrities raving about the importance of good skincare to their audiences. Most people don’t pay much attention to it, just splashing their face with water and soap and calling it a day, while some others worship the ten-step Korean skincare regimens popularized in East Asia.

So, is there something to the hype of skincare? Or is it all just a marketing gimmick to sell you products you don’t really need?

The answer is - a bit of both.

Before we get into what’s in our skincare products, let’s explore some basics about skin biology:

The biology of our skin

Our skin is made up of three main layers, namely the epidermis, the dermis, and the subcutaneous tissue. The epidermis is the outermost layer of skin and is what protects us from most invading pathogens and other environmental stressors. The dermis is below the epidermis, and it is a much thicker layer containing blood vessels, sweat glands, sebaceous glands, and hair follicles amongst other things. The subcutaneous tissue below the dermis is where we store fat (called adipose).

Figure 1: The anatomy of our skin.

Collagen is the main protein component of the dermis; it is responsible for maintaining its strength and elasticity. Meanwhile, elastin and keratin are the two other essential proteins found in our skin. As we grow older, the cellular process involved in collagen and elastin production become less and less efficient, and this is how we develop fine lines and wrinkles.

The key to having good skin is by providing optimal nourishment and moisture to the dermis, as this is where the critical components of the skin are located. The best way to do this is through your diet, and to have sufficient water intake. However, due to the increase in pollution, stress, and other external factors in our modern world, the skin is fighting an outward battle as well – resulting in common skin concerns like acne, dark spots, pigmentation, redness, sensitivity, and clogged pores.

Skin types

There are three basic skin types - oily, dry, and normal. With that in mind, having combination skin means you tend to have a different skin type on a different part of your face. For example, many people tend to have oily T zones, which is the area around the forehead and nose. In essence, your skin type usually influences what type of products your skin will tolerate and respond well to (more on this later).

The science behind the skincare – active ingredients

So, what makes these products actually do what they claim to be able to do? And how do they work at the cellular level?

Let’s take a look at the science behind some popular skincare products…


Cleansers are formulations which dissolve and clear impurities from the skin. This is also commonly known as face wash. They can be oil-based or water-based.

Cleansers work in a similar way to traditional bar soap, but they are less drying and do not strip the skin of moisture. They are also optimised to maintain the skin’s surface pH (<5). Cleansers contain molecules known as ‘surfactants’, which are composed of a lipophilic and hydrophilic molecular group. Lipophilic means ‘oil/fat loving’, and hydrophilic means ‘water loving’. Hence the surfactant is able to attract the oil-based impurities like sebum and dirt by the lipophilic group and then let them be washed off by water, which is attracted to the hydrophilic group.

Figure 2: A surfactant molecule

Cleansers often contain some moisturising ingredients to prevent stripping the skin and making it dry and irritated, unlike what some harsher soaps do. This is why it is recommended to have a separate face wash from your regular body wash or soap.


Serums contain highly concentrated active ingredients to target particular skincare concerns like dark spots, wrinkles, fine lines, dullness, or redness. They usually contain only one or two active ingredients. An essence is another product which contains just a few active ingredients and is usually a less concentrated version of a serum.

Here are some of the common active ingredients of serum and their functions:

  • Vitamin C: Essential for collagen synthesis, influences gene expression of antioxidant enzymes, promotes the formation and differentiation of the epidermal layers.

  • Vitamin E: A free radical scavenger. Free radicals are extremely reactive molecules produced when skin is exposed to sunlight and other stressors. These free radicals interact with the DNA/RNA and proteins in the skin and can cause them to malfunction.

  • Retinol: A group of vitamin A derivatives that promote the proliferation of the epidermis, influences the even distribution of melanin (a natural skin pigment) in our skin, and protects collagen from degradation. Retinol and retinoids are suitable for use at night, as during the day they are broken down by sunlight. In fact, retinoids are some of the most potent skincare active ingredients with scientifically proven benefits for skin.

  • Hyaluronic acid: A glycosaminoglycan found in connective and epithelial tissue. It is widely present in the extracellular matrix of basal keratinocytes in the epidermis and plays a role in cell proliferation and free radical scavenging. Its main role in skincare products is as a tissue hydrator.

  • Alpha hydroxy acids (AHA): These are compounds which exfoliate the skin (i.e. they help remove the top layer of dead skin cells). Some common AHAs found in skincare products are glycolic acid, lactic acid, and citric acid. In general, AHAs increase the amount of collagen and glycosaminoglycans in the dermis.

  • Beta hydroxy acids (BHA): BHA in skincare usually refers to salicylic acid (2-hydroxybenzoic acid). Salicylic acid is a more potent exfoliator than AHAs and can penetrate deeper into the dermis. It has keratolytic action (i.e. involved in the lysis of keratinocytes, which are cells found in the epidermis). It also breaks down desmosomes, which are proteins in the junctions between cells that hold tissue together. Hence, salicylic acid helps the top layer of skin ‘slough off’ and reveal the new skin beneath.

These are just a few of the common active ingredients found in many serums and other skincare formulations.


A toner is a water-like liquid containing active ingredients. It can have a variety of functions including hydration, exfoliation, brightening, and soothing. Toners have a lower concentration of active ingredients overall when compared to serums and essences and are usually more suited for daily use.


Physical- or chemical-based formulations which help slough off dead skin cells and reveal new, fresh skin are called exfoliators.

Physical exfoliants are usually composed of tiny particles that cause abrasion against the skin in order to physically remove dead skin cells. Physical exfoliators tend to only work on the surface of the skin, rarely penetrating into the dermis layer. These provide an instant exfoliating effect but can be harsh on sensitive skin. Microplastic beads are an example of physical exfoliators that are gentler than the abrasive particles but have the added downside of causing plastic pollution.

AHAs and BHAs (as mentioned in the previous section) are chemical exfoliators which are extremely effective at working in the deeper layers of the skin due to their small molecular size. At low concentrations (10% for AHA, less than 2% for BHA), they can be used daily over the long term to show positive results. Whereas at high concentrations (30% AHA, >2% BHA), they are used as chemical peels, which are done far less frequently (not more than three times per week). This is because these exfoliating acids can be potentially damaging to skin at high concentrations.


The most well-known component of skincare, moisturisers are creamy formulations which lock in moisture (obviously!) and hydrate the skin barrier. The key ingredient in moisturisers are humectants, which are molecules that possess many hydrophilic (‘water loving’) groups. The presence of these chemical groups allows them to attract moisture from the surroundings. Some common humectants found in skincare are glycerin, hyaluronic acid (and its derivatives like sodium hyaluronate), propylene glycol, butylene glycol, and sorbitol.


Sunscreens are creamy formulations with active sun protection ingredients that block or absorb UV radiation. In particular, the two types of radiation which cause damage to our skin are UVA and UVB.

Both UVA and UVB penetrate the skin and cause a myriad of skin-damaging effects. For instance, UV radiation interacts with oxygen in our cells to produce a radical molecule called a superoxide. Free radicals are molecules which contain an unpaired electron in the valence shell, thus making them extremely reactive. These free radicals interact with the macromolecular structures in cells (such as DNA, RNA, and proteins) and alter their native structure, thus causing them to malfunction. In contrast, an antioxidant is a compound which is able to ‘quench’ the free radical by donating an electron to the unpaired one, thus stabilising the molecule. Hence, this is why antioxidants are touted as protective ingredients in both food and skincare.

When UV radiation hits keratinocytes in the epidermis, it causes cellular damage whereby the damaged cells initiate a signalling cascade. This results in the upregulation of enzymes involved in melanin biosynthesis within melanocytes. And the final appearance of this is what we commonly known as having a ‘tan’. The tan is actually the body trying to protect itself from further UV damage, however this is not as effective as having an SPF on your skin.

UVB radiation also interacts with 7-dehydrocholesterol to eventually produce vitamin D3, a critical vitamin for immune, skeletal, and metabolic health.

There are two main types of sunscreen – mineral and chemical.

Figure 3: The mechanism of physical and chemical sunscreens.

Mineral sunscreens create a physical barrier that reflect UV light, whilst chemical sunscreens absorb the radiation (instead of reflecting it) and convert it to heat energy. Both sunscreens are generally effective, however several chemical sunscreen ingredients like oxybenzone (which absorbs UVA) and octyl salicylate (absorbs UVB) have been linked to coral bleaching and reef damage. There is also some evidence that chemical sunscreens can cause allergic reactions and worsen certain skin conditions like redness and pigmentation as it gets absorbed into our skin.

On the other hand, zinc oxide and titanium oxide are the most common ingredients in mineral sunscreens and are safe to use on skin. Additionally, when the particles are larger than 100 nm, they are considered coral-safe. The one downside of mineral sunscreens is that they tend to create a white film (‘white cast’) on the skin and can feel rather thick on our skin (as they form a protective layer).

Concluding remarks – what’s right for your skin?

From the scientific analysis of skincare products outlined above, it is clear to see that formulations contain ingredients with biochemical properties which actually do what they claim to do.

But the question remains, do you really need a seven-step routine in the morning and evening to achieve ideal skin? The simple answer is no, you don’t need so many products/steps in your routine to achieve healthier skin, but there are some products which are essential in a morning routine:

  • A cleanser for your skin type (normal, dry, oily, combination)

  • An exfoliator (two to three times a week)

  • A moisturiser

  • A sunscreen (ideally mineral)

Exfoliators can come in many concentrations and formulations (e.g. serums, toners, wash off peels, creams). Using an exfoliator keeps your pores clean and helps your skin barrier renew itself. It is important to use sunscreen whenever you use an exfoliator in order to protect your newly revealed layer of skin from UV damage. Sunscreen is the most important component of any daytime skincare routine, as it protects from UV damage (detailed in the previous section).

Your night-time routine can consist of the same products without the sunscreen (for fairly obvious reasons). With consistent use, even a simple routine as described above can give you great results!

If you have a particular skin condition like acne, dullness, pigmentation, uneven texture, or blackheads, you can consider using a serum, toner, or other product containing specific active ingredients:

  • Acne – use products containing AHAs, BHAs and niacinamide (vitamin B derivative)

  • Dullness – vitamin C/E, hyaluronic acid

  • Blackheads – BHAs

  • Pigmentation – retinol, vitamin C, other antioxidant extracts

  • Uneven texture – retinol, AHAs

But always bear in mind, some products can cause a reaction (e.g. to sensitive or sensitized skin), so it is important to patch test them (e.g. on your arm) before use.

Having a skincare routine does not necessarily have to be as expensive or laborious as it is made out to be. In fact, expensive does not always mean better! Some affordable and effective skincare brands include CeraVe, The Ordinary, The InkeyList, Sukin, and La Roche-Posay.

All in all, I hope this article has shed some light on skincare formulations and given you some knowledge to curate your own skincare routine. And just for the fun of it, here’s my own skincare routine(!):

  • Micellar Water from Avene (to remove makeup)

  • Rose & Jasmine Cleanser from Kama Ayurveda

  • Rose Tonic from Pixi (used in the morning)

  • AHA BHA PHA 30 Days Miracle Toner from Some by Mi (used only at night)

  • Rice & Ceramide Moisturise Emulsion from The Face Shop

  • Soltan Protect & Moisturise Spray SPF 30 from Boots (used in the morning)

Author: Devyani Saini, MRes Molecular & Cellular Biosciences

Disclaimer: in2biochem was not sponsored by Avene, Kama Ayurvesa, Pixi, Some by Mi, CeraVe, The Ordinary, The InkeyList, Sukin, The Face Shop, Boots, or La Roche-Posay for this article.


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