Skincare ingredients that work - evidence-based guide | Nordic Skin College
The skincare market is overflowing with products promising miracles. New ingredients appear every month, and it can be difficult to distinguish between genuine effect and pure marketing. But there is actually a relatively short list of active ingredients with solid scientific evidence behind them.
Here we review the seven best-documented active ingredients - what they do, who benefits from them, and how to use them correctly.
Retinol (Vitamin A)
Retinol is the most studied anti-ageing ingredient in the history of skincare. It is a form of vitamin A that converts to retinoic acid in the skin, where it stimulates cell turnover and collagen production.
What it does
Retinol increases cell turnover in the outermost layer of the skin, which over time smooths fine lines, reduces pigmentation changes and improves skin texture. It also stimulates collagen in the dermis, giving the skin firmness.
Who benefits from it
Everyone over 25-30 who wants to prevent or reduce signs of ageing. It is also effective against acne, because it prevents clogging of pores.
How to use it
Start low (0.3-0.5%) and use it 2-3 times a week in the evening. Gradually increase to daily use over 4-8 weeks. Always use SPF during the day, as retinol makes the skin more light-sensitive.
Combine with
Hyaluronic acid and ceramides (counteracts dryness). Niacinamide can be used in the same routine and reduces irritation.
Avoid combining with
AHA/BHA acids on the same evening (too much exfoliation). Benzoyl peroxide (inactivates retinol). Vitamin C at high concentrations (too irritating together, but can be used morning/evening separately).
Niacinamide (Vitamin B3)
Niacinamide is one of the most versatile ingredients in modern skincare. It is tolerated by almost all skin types and has an impressively broad range of effects.
What it does
Niacinamide strengthens the skin barrier by boosting ceramide production. It regulates sebum production, reduces redness and inflammation, evens out skin tone and minimises the visibility of pores. It also inhibits the transfer of melanin to the skin’s surface, reducing pigmentation marks.
Who benefits from it
Practically everyone. Particularly relevant for oily and blemish-prone skin, sensitive skin with redness, skin with uneven tone or dark spots, and as a supplement for retinol users.
How to use it
Concentrations of 2-5% are optimal. Can be used morning and evening. Apply after cleansing and toner, before heavier products.
Combine with
Everything. Niacinamide is one of the most compatible ingredients and can be combined with retinol, vitamin C, AHA/BHA and hyaluronic acid without problems.
Hyaluronic acid
Hyaluronic acid is not an acid in the traditional sense - it does not exfoliate. It is a sugar molecule that occurs naturally in the skin and can bind up to 1,000 times its own weight in water.
What it does
It attracts and retains moisture in the skin, giving a plumping effect and reducing the visibility of fine lines. Different molecular sizes penetrate different layers of the skin: high molecular weight sits on the surface and provides immediate hydration, while low molecular weight penetrates deeper.
Who benefits from it
All skin types, including oily skin. Particularly beneficial for dehydrated skin (which is a condition, not a skin type - even oily skin can be dehydrated).
How to use it
Apply to damp skin and seal the moisture in with a cream or oil afterwards. In very dry climates, without this sealing step, hyaluronic acid can actually draw moisture up from deeper skin layers instead of from the air.
Combine with
Everything. Hyaluronic acid functions as a moisture boost under all other active ingredients.
Vitamin C (L-ascorbic acid)
Vitamin C is a potent antioxidant that protects the skin from free radicals caused by UV radiation and pollution. The most active form is L-ascorbic acid.
What it does
Neutralises free radicals, stimulates collagen production, inhibits melanin production (lightens pigmentation marks) and boosts the effectiveness of sun protection. It also gives the skin a visible glow.
Who benefits from it
Everyone who wants to protect their skin from environmental damage and ageing. Particularly relevant for smokers, people living in polluted urban environments, and those with pigmentation concerns.
How to use it
Use a serum with 10-20% L-ascorbic acid in the morning under your SPF. Start with a lower concentration if you have sensitive skin. Store it in a dark, cool place - vitamin C oxidises easily (you can tell because the product turns brown/orange).
Combine with
SPF (enhances sun protection). Vitamin E and ferulic acid (stabilises vitamin C and increases its effectiveness). Hyaluronic acid.
Avoid combining with
Niacinamide at very high concentrations (over 10% of each) can cause temporary redness in some people, but at the concentrations found in products, this is rarely an issue.
AHA and BHA (chemical acids)
AHA (alpha-hydroxy acids) and BHA (beta-hydroxy acids) are chemical exfoliants that remove dead skin cells without physical scrubbing.
What they do
AHA (glycolic acid, lactic acid, mandelic acid) dissolves the bonds between dead skin cells on the surface. This gives smoother texture, more even skin tone and better product absorption. Want to experience AHA in a professional setting? Try our AHA fruit acid treatment at the student clinic.
BHA (salicylic acid) is oil-soluble and therefore penetrates into the pores, where it dissolves sebum and dead cells. It is anti-inflammatory and is preferred for blemish-prone and oily skin.
Who benefits from them
AHA: dry, sun-damaged and mature skin with uneven texture. BHA: oily, blemish-prone skin with clogged pores and spots.
How to use them
Start with low concentrations (AHA 5-8%, BHA 1-2%) 2-3 times a week. Gradually increase the frequency. Always use SPF the following day, as the skin becomes more light-sensitive.
Combine with
Hyaluronic acid and ceramides (rebuilds the barrier after exfoliation). Niacinamide (soothing).
Avoid combining with
Retinol on the same evening. Other exfoliation (physical scrubs). Other acids at high concentrations.
Ceramides
Ceramides are lipids (fats) that naturally make up about 50% of the skin’s barrier layer. They are not “active” in the traditional sense - they rebuild the skin’s own structure.
What they do
Ceramides repair and strengthen the skin barrier, which is your primary defence against moisture loss, irritants and microorganisms. An intact barrier means less dryness, less irritation and better tolerance of active ingredients.
Who benefits from them
Everyone - but particularly dry, sensitive and irritated skin. Indispensable for eczema-prone skin and rosacea-prone skin. Also important as a supplement when using retinol or chemical acids that temporarily weaken the barrier.
How to use them
Ceramides work best together with cholesterol and free fatty acids in a ratio that mimics the skin’s natural composition. Choose products that contain all three. Use them as your moisturiser or as an extra step after active ingredients.
Combine with
Everything. Ceramides are a foundational step, not an active treatment. They support all other ingredients by keeping the barrier intact.
Peptides
Peptides are short chains of amino acids that function as signalling molecules in the skin. They “communicate” with the skin’s cells and can stimulate specific processes.
What they do
Different peptides have different functions: some stimulate collagen production (such as Matrixyl), others reduce muscle tension (such as Argireline), and some strengthen the skin barrier. They are generally milder than retinol with fewer side effects, but the effect is also more moderate.
Who benefits from them
Those who want anti-ageing benefits but cannot tolerate retinol. Sensitive skin that needs a gentle approach. As a supplement to an existing anti-ageing routine.
How to use them
Peptides are stable and can be used morning and evening. They work best in serum form, where the concentration is highest.
Combine with
Hyaluronic acid, niacinamide, ceramides. Can be used together with retinol at different times.
Avoid combining with
Direct AHA/BHA at high concentrations (acidic pH levels can break down peptide bonds).
How to build a routine with active ingredients
The most important rule: introduce one new ingredient at a time and give it 2-4 weeks. This way you can isolate any reactions and feel the effect.
Unsure what your skin needs? A personal skin analysis and consultation gives you professional guidance on the right ingredients for your particular skin.
A solid base routine for most people:
Morning: Cleanser - Vitamin C serum - Moisturiser with niacinamide - SPF
Evening: Cleanser - Retinol OR AHA/BHA (never both) - Moisturiser with ceramides
Remember that active ingredients take time. Retinol and vitamin C require 8-12 weeks of consistent use before you see clear results. Hyaluronic acid and ceramides give faster visible effects, often within days.
Knowledge makes the difference
At Nordic Skin College we teach our cosmetology students the biology and chemistry of the skin, so they can advise clients with professional depth - not just repeat product descriptions. Want to understand skincare at a professional level? See our programmes and become the expert others turn to for advice.