How Does Our Skin Work? – The Scientific Foundations of Skincare

Many people dive straight into skincare by searching for products, learning about ingredients, and building routines — but they skip one of the most important steps: understanding how the skin actually works. Once you know this, a lot falls into place: why one cream is effective and another doesn't work, why layering matters, and why timing your products isn't arbitrary.

The Three Layers of Skin

Skin isn't a simple wrapper — it's the largest organ in the body, made up of three distinct layers.

Epidermis – the visible line of defence

The epidermis is the outermost layer, the one you see and touch. It's made up mainly of keratinocytes, which constantly renew themselves: they originate in the deeper layers, travel upward, and eventually shed at the surface. This process takes around 28 days — the so-called skin cell turnover cycle.

The topmost part of the epidermis is called the stratum corneum (the horny layer). This is the true barrier: it prevents harmful substances, bacteria, and UV radiation from penetrating the body, while also controlling water loss. If this layer is damaged or weakened, the skin becomes dehydrated and sensitive.

The epidermis also contains the Natural Moisturising Factor (NMF) — a mix of amino acids, lactic acid, and other water-binding molecules that help the skin retain moisture. Many moisturisers mimic or replenish these substances.

Dermis – the source of elasticity

The dermis sits beneath the epidermis and is considerably thicker. This layer gives the skin its firmness and flexibility, made up primarily of collagen and elastin fibres.

• Collagen provides the structural integrity of the skin. It's produced abundantly when we're young, but from the mid-twenties onward, it decreases by around 1% per year.
• Elastin ensures the skin stays supple and snaps back into shape.
• Hyaluronic acid is a molecule naturally present in the dermis, capable of holding many times its weight in water — it's responsible for the skin's plumpness and hydration.

Hypodermis – the foundation

The deepest layer consists mainly of fat cells and connective tissue. It cushions and protects deeper organs, plays a role in temperature regulation, and acts as an energy reserve. Skincare products typically don't reach this layer.

What Does the Skin Do?

Skin isn't passive — it actively works to keep you healthy:

• Protection: Keeps out bacteria, chemicals, UV radiation, and physical damage.
• Temperature regulation: Controls body temperature through sweating and adjusting blood flow.
• Sensation: Through nerve endings, it detects touch, pain, heat, and cold.
• Vitamin D synthesis: Under UV exposure, it produces vitamin D, which is essential for bone health and immune function.

Why Does This Matter for Skincare?

Knowing how the skin is structured makes ingredients and products far easier to understand:

• Most active ingredients (e.g. hyaluronic acid, niacinamide, peptides) only reach the epidermis — they don't enter the bloodstream and don't affect the body.
• Retinol and chemical exfoliants (AHA, BHA, PHA) work by accelerating cell turnover, meaning they intervene in the epidermis's natural renewal cycle.
• SPF protects the epidermis from UV damage, which is one of the main drivers of collagen breakdown.
• Moisturisers supplement the NMF and help maintain the skin's protective barrier.

Summary

The skin is a complex, layered system, and understanding it is the first step toward truly informed skincare. You don't need to be an expert to make better decisions — you just need to know which layer does what, and how it responds to different ingredients. That's the foundation for everything else I write about on this blog.