An active ingredient is the one doing the actual work — the component shown to change something about your skin, rather than the ones that make a product spreadable, stable or pleasant to use. Everything else in the bottle supports it.
That is the whole concept. The confusing part is that there are perhaps a dozen actives worth knowing, marketing implies there are hundreds, and some of them should not be used together.
The ones worth knowing
Salicylic acid (BHA)
Does: dissolves oil and dead skin inside the pore.
Best for: blackheads, clogged pores, oily skin.
Typical strength: 0.5–2% over the counter.
Note: oil-soluble, which is why it reaches into pores when water-soluble acids cannot.
Glycolic and lactic acid (AHAs)
Does: loosens dead cells on the surface.
Best for: dullness, rough texture, uneven tone.
Note: glycolic has the smallest molecule and penetrates most, which also makes it the most irritating. Lactic is gentler and more hydrating.
Benzoyl peroxide
Does: kills the bacteria involved in inflammatory acne.
Best for: red, painful spots.
Typical strength: 2.5–10%. Studies have repeatedly found 2.5% about as effective as 10% with much less irritation.
Note: bleaches fabric permanently.
Retinoids
Does: speeds up skin cell turnover; the best-evidenced ingredient in skincare.
Best for: acne, texture, long-term skin ageing.
Forms: retinol and retinaldehyde over the counter, adapalene over the counter in the US, tretinoin on prescription.
Note: start twice a week. Nightly from day one is the most common self-inflicted skincare injury.
Niacinamide
Does: supports the skin barrier, helps regulate oil, reduces redness and post-acne marks.
Best for: almost everyone; one of the best-tolerated actives.
Typical strength: 4–5%. Higher is not better and above about 10% can itself irritate.
Vitamin C (L-ascorbic acid)
Does: antioxidant; helps with dark marks and dullness.
Note: unstable. If yours has turned dark orange it has oxidised and is no longer doing much.
Azelaic acid
Does: works on both acne and redness, and on post-acne pigmentation.
Best for: people whose skin cannot tolerate the harsher options.
Sunscreen filters
Worth naming, because sunscreen is an active product and the only one that prevents the damage the others spend their time correcting.
What is not an active
Glycerin, hyaluronic acid, ceramides, squalane and most oils are hydrators and barrier ingredients. They are useful — often more useful than another active — but they are not changing skin function, and they can be used freely alongside almost anything.
What not to combine
| Combination | Why not |
|---|---|
| Retinoid + AHA/BHA in the same routine | Compounding irritation; alternate nights instead |
| Benzoyl peroxide + retinol, same application | Can deactivate the retinol; use at different times of day |
| Vitamin C + AHA/BHA together | Tolerated by some, stinging for many; separate them morning and night |
| Two or more exfoliating acids | No added benefit, much added risk |
Niacinamide, by contrast, is fine with essentially everything. The old claim that it cancels out vitamin C came from research conducted at high heat and does not apply to finished products at room temperature.
How to read a percentage
A higher number is not a better product. What matters is the percentage, the formula’s pH, how it is delivered and whether your skin tolerates it. A well-formulated 0.5% retinol will out-perform a 1% that you abandon after a week because it stung.
Ingredient lists are ordered by quantity down to 1%, after which order means nothing. So an active listed near the end is not necessarily present in a meaningless amount — many actives work at well under 1%.
How many should you use?
At the start, one. Give it eight to twelve weeks. Add a second only if there is a different problem the first does not address. Most people get the majority of their results from one active, a moisturiser and daily sunscreen.
General information, not medical advice. For ingredient guidance see the American Academy of Dermatology.
Related: purging or breakout? and the four-step routine.