Serums deliver a significantly higher concentration of active ingredients than standard moisturisers, targeting specific skin concerns more directly and preparing the skin to absorb everything that follows. Anti-ageing, deep hydration, brightening, pore-minimising — the results depend on what is inside the bottle. Here is how face serums work, which types exist, and how to use them correctly.
How Does a Face Serum Work?
The key difference between a serum and a moisturiser lies in molecular size and concentration. Serums use a lighter, water-based or oil-based carrier with smaller molecules that can penetrate deeper into the skin layers, delivering a much higher dose of active compounds than a standard cream can. Where a moisturiser primarily works on the skin surface to seal in hydration and provide a protective barrier, a serum works further down — at the level of the dermis — where it can influence collagen production, cellular turnover, pigmentation, and moisture retention more directly.
This is why serum is applied before moisturiser, not instead of it. The serum handles the targeted, active work; the moisturiser locks in that work and provides the protective finish. Skipping the moisturiser after serum leaves the skin exposed; applying serum on top of a moisturiser renders it largely ineffective as the heavier cream blocks penetration.
Types of Face Serum: Which One Do You Need?
Hydrating Serum (Hyaluronic Acid)
Hyaluronic acid (HA) is the gold standard hydrating ingredient — a naturally occurring molecule that can hold up to 1,000 times its weight in water. Serum-level HA concentrations deliver immediate plumping, smoothing, and moisture-binding effects that persist throughout the day or night. This is the most universally appropriate serum type: suitable for all skin types, including sensitive and acne-prone, and an excellent starting point for anyone new to serums. Results are visible quickly — typically within a week of consistent use. Best applied to slightly damp skin for maximum absorption.
Vitamin C Serum
The most widely used active for brightening and anti-ageing, vitamin C has strong antioxidant properties that help neutralise free radical damage caused by UV exposure and pollution — the primary drivers of premature skin ageing. It also inhibits melanin production, which means regular use can visibly reduce dark spots, uneven tone, and post-acne marks over time. Additionally, vitamin C is essential for collagen synthesis, making it one of the most evidence-backed actives for long-term skin quality. Morning application (before SPF) is generally recommended for maximum antioxidant protection during the day.
Niacinamide Serum
Niacinamide (vitamin B3) is one of the most versatile and well-tolerated actives available. It regulates sebum production, minimises the appearance of enlarged pores, improves skin texture, reduces redness, and helps fade hyperpigmentation — all without the irritation associated with stronger actives like retinol or acids. Concentrations of 10–20% are widely used in K-Beauty formulations, often combined with zinc (for acne-prone skin) or tranexamic acid (for targeted dark spot correction). Suitable for morning and evening use.
Retinol Serum
Retinol (vitamin A) is the most clinically validated anti-ageing active in cosmetics. It accelerates cellular turnover, stimulates collagen production, and significantly reduces the appearance of fine lines, wrinkles, and sun damage with consistent use. It requires a careful introduction — starting at lower concentrations (0.5–1%) and gradually building frequency — as it can initially cause dryness and sensitivity. Evening-only use is standard, as retinol is destabilised by UV light. Not recommended during pregnancy.
Acne and Blemish-Targeting Serum
Serums formulated for acne-prone skin typically combine antibacterial actives (such as tea tree oil, zinc, or salicylic acid) with soothing compounds (centella asiatica, panthenol, madecassoside) to address active breakouts while repairing the skin barrier. These are best used in the evening as spot treatments or as a full-face serum when the entire skin is reactive. Overuse or combining too many actives at once is the most common mistake — when starting a blemish serum, simplify the rest of the routine.
[tip:Introduce only one new serum at a time and use it consistently for at least 4–6 weeks before assessing results. Most actives — especially vitamin C, niacinamide, and retinol — show their best effects after 8–12 weeks of regular use. Switching too quickly or layering too many serums at once makes it impossible to know what is working.] [products: cosrx-hyaluronic-acid-hydra-power-essence-100-ml, cosrx-the-vitamin-c-serum-20-ml, isntree-hyper-niacinamide-20-serum-20-ml, isntree-hyper-retinol-ex-1-0-serum-20-ml, beauty-of-joseon-serum-with-propolis-niacinamide-glow-30-ml, axis-y-dark-spot-correcting-glow-serum-50-ml, cos-de-baha-nz-niacinamide-20-zinc-pca-4-serum-30-ml, numbuzin-no-3-skin-softening-serum-50-ml]
How to Apply a Face Serum: Step-by-Step
Correct application is as important as choosing the right serum. Even the best formulation will underperform if applied incorrectly:
- Remove all makeup thoroughly — any residue left on the skin forms a physical barrier that prevents the serum from penetrating. Double cleansing (micellar water or cleansing oil first, then a gentle gel or foam cleanser) ensures a clean canvas.
- Deep cleanse — follow up with your regular cleanser. If using a chemical exfoliant (AHA/BHA toner or mask), use it at this stage rather than after the serum.
- Apply toner — hydrating toners prepare the skin for serum absorption, particularly for hyaluronic acid-based products which work best on slightly damp skin.
- Apply the serum — use the recommended amount (typically 3–5 drops or a pea-sized amount). Warm it between your fingertips first, then press gently into the skin using circular motions. Avoid dragging or rubbing.
- Wait, then moisturise — allow 5–10 minutes for the serum to absorb, then apply your moisturiser to seal in the active ingredients. In the morning, follow with SPF.
Morning vs Evening Serum: When to Apply?
Evening application is typically more effective for the majority of active serums. At night, the skin enters its regenerative phase — cellular repair accelerates, blood flow to the skin increases, and absorption of active compounds is generally higher. There are also no UV or environmental stressors to contend with, which matters for photosensitive actives like retinol and vitamin C (in some formulations).
Morning application suits antioxidant serums — particularly vitamin C — which provide protection against daytime UV and pollution damage when used alongside SPF. A hydrating serum can also be used in the morning as a base for makeup, providing a smoothing, plumping effect that improves foundation application. For those with very depleted or reactive skin, using the same hydrating serum both morning and evening is a good way to accelerate results. Avoid applying two separate potent actives (e.g., retinol and vitamin C) in the same session — use one in the morning and one at night instead.
[warning:Do not combine retinol with high-percentage vitamin C, AHA acids, or benzoyl peroxide in the same routine session — this significantly increases the risk of irritation. If you want to use multiple actives, alternate them: acids or vitamin C in the morning, retinol in the evening. Always patch test a new serum on the inner arm before applying it to the face.]
K-Beauty Serums: A Different Approach
Much of the modern serum landscape has been shaped by Korean skincare philosophy, which treats the skin as something to be maintained preventively rather than corrected reactively. K-Beauty serums typically feature gentler but highly effective formulations — layered in multiple thin steps rather than applied in one heavy dose. This approach prioritises skin barrier integrity alongside active ingredient delivery, which is why K-Beauty serums are often better tolerated by sensitive skin than their Western equivalents at equivalent active concentrations. Explore our full facial acids, oils and serums collection and the broader facial cosmetics range for the complete selection available at Medpak.
[products: mixsoon-bean-face-essence-50-ml, anua-niacinamide-10-txa-4-dark-spot-removing-serum-30-ml, cosrx-refresh-aha-bha-vitamin-c-booster-serum-20-ml, vt-cosmetics-reedle-shot-lifting-serum-30-ml, mary-may-multi-hyaluronics-serum-30-ml, isntree-hyper-vitamin-c-23-serum-20-ml, cos-de-baha-h-hyaluronic-acid-serum-60-ml, pyunkang-yul-moisture-serum-100-ml] [note:All Medpak orders ship from within the EU — no customs fees, no long wait times. Fast, reliable delivery across Europe.]
