Ingredient glossary
Every skincare word, in one plain sentence
Labels are written for chemists. This is the same vocabulary written for the person actually standing at the sink — what an ingredient does, when it belongs in a routine, and what it is worth beside.
The short answer
Search a word below to get its definition, whether it belongs in the morning or the evening, and any pregnancy note. The same lookup sits inside every step of your own routine, so you never have to leave the page you are reading.
Written by Lumen Ritual · Last updated:
Content is reviewed periodically for accuracy and updated as needed. How we research routines

43 terms
Allergy-safe mode
Nothing on your avoid list yet. Add ingredients you react to in the quiz, and this page will flag them for you. Set your avoid list.
A
actives
JargonThe ingredients doing measurable work — acids, retinoids, vitamin C. One new active at a time, always.
Also called: active
Build my routine to see where this fits.
adapalene
PMActiveA prescription-strength retinoid sold over the counter for acne. Stable alongside benzoyl peroxide, unlike retinol.
Pregnancy Avoided in pregnancy along with the rest of the retinoid family.
Also called: differin
Build my routine to see where this fits.
alpha arbutin
EitherActiveA gentle brightener for dark marks. Slower than acids, and far less likely to irritate.
Also called: arbutin
Build my routine to see where this fits.
azelaic acid
EitherActiveCalms visible redness and post-spot marks without the sting most actives bring to reactive skin.
Build my routine to see where this fits.
B
barrier
BarrierThe outermost layer that keeps water in and irritants out. When it is damaged, everything stings.
Also called: moisture barrier, skin barrier
Build my routine to see where this fits.
benzoyl peroxide
EitherActiveAn antibacterial that clears active spots quickly. It bleaches fabric, so keep it away from good towels.
Also called: bp, bpo
Build my routine to see where this fits.
broad spectrum
AMSun careSunscreen that filters both UVB (burning) and UVA (ageing) light. Anything less is half a sunscreen.
Build my routine to see where this fits.
buffering
PMMethodApplying moisturiser before a retinoid so it works more gently. Costs a little strength, saves a lot of peeling.
Build my routine to see where this fits.
C
centella
EitherBarrierCica. A soothing botanical used to settle redness and support healing after actives.
Also called: cica, centella asiatica, madecassoside
Build my routine to see where this fits.
ceramides
EitherBarrierThe lipids your barrier is built from. Replacing them is what stops the tight, flaky feeling.
Also called: ceramide
Build my routine to see where this fits.
chemical filter
AMSun careUV filters that absorb light rather than sitting on top. Lighter and clearer on the skin, and better on deeper tones.
Also called: organic filter, avobenzone, tinosorb
Build my routine to see where this fits.
comedone
JargonA blocked pore. Open ones read as blackheads, closed ones as the small bumps under the surface.
Also called: blackhead, closed comedone
Build my routine to see where this fits.
D
double cleanse
PMMethodAn oil or balm first to lift sunscreen and makeup, then a water-based wash. Evenings only.
Also called: oil cleanse
Build my routine to see where this fits.
F
fragrance-free
JargonNo fragrance added at all. Not the same as unscented, which can use masking fragrance to hide a base smell.
Also called: unscented, parfum
Build my routine to see where this fits.
G
glycerin
EitherHydratorThe quiet workhorse humectant. Cheap, non-irritating and in almost every good moisturiser.
Also called: glycerol
Build my routine to see where this fits.
glycolic acid
PMActiveThe smallest AHA, so it penetrates fastest. Strong on dullness and texture, and the most likely acid to sting.
Also called: aha, alpha hydroxy acid
Build my routine to see where this fits.
H
humectant
HydratorAn ingredient that draws water into the skin — glycerin and hyaluronic acid are the common ones.
Build my routine to see where this fits.
hyaluronic acid
EitherHydratorA humectant that holds water in the upper skin. Apply to damp skin and seal it with moisturiser.
Also called: sodium hyaluronate, ha
Build my routine to see where this fits.
hyperpigmentation
JargonPatches darker than your base tone — from spots, sun or inflammation. Slow to fade, and SPF decides the pace.
Also called: dark marks, pih, post-inflammatory hyperpigmentation
Build my routine to see where this fits.
L
lactic acid
PMActiveA gentler AHA that hydrates while it exfoliates. A sensible first acid if glycolic feels sharp.
Build my routine to see where this fits.
M
mandelic acid
PMActiveA large, slow AHA. The kindest acid for reactive or deeper skin tones because it works evenly rather than fast.
Build my routine to see where this fits.
N
niacinamide
EitherActiveVitamin B3. Calms redness, steadies oil and supports the barrier. Sits happily beside almost anything.
Also called: vitamin b3, nicotinamide
Build my routine to see where this fits.
non-comedogenic
JargonFormulated not to block pores. Useful shorthand, though it is not a regulated claim.
Build my routine to see where this fits.
O
occlusive
BarrierA sealing layer, like squalane or petrolatum, that stops water escaping overnight.
Build my routine to see where this fits.
P
panthenol
EitherBarrierProvitamin B5. Soothes and helps a stressed barrier recover — common in post-active repair creams.
Also called: provitamin b5, vitamin b5
Build my routine to see where this fits.
patch test
MethodTrying a new product on a small area for a few days before it goes near your whole face. Worth the wait.
Build my routine to see where this fits.
peptides
EitherActiveShort chains of amino acids that support firmness. A gentle partner while you build retinoid tolerance.
Also called: peptide, copper peptides, matrixyl
Build my routine to see where this fits.
ph
JargonHow acidic a formula is. Skin sits around 4.7–5.5; acids work low, and a very high-pH wash leaves skin tight.
Build my routine to see where this fits.
pha
PMActivePolyhydroxy acid — gluconolactone and lactobionic acid. Exfoliates the surface only and holds water while it does it.
Also called: polyhydroxy acid, gluconolactone
Build my routine to see where this fits.
purging
JargonA short flare as accelerated cell turnover clears existing congestion. Lasts weeks, not months, and only in usual breakout areas.
Build my routine to see where this fits.
R
retinoid
PMActiveThe family name for retinol and its prescription relatives — the best-studied ingredient for lines and texture. Evenings only.
Pregnancy Retinoids are avoided in pregnancy. Azelaic acid is the usual stand-in.
Also called: tretinoin, retinaldehyde, retinal
Build my routine to see where this fits.
retinol
PMActiveThe over-the-counter retinoid. Start twice a week at night and build up slowly.
Pregnancy Not used in pregnancy — swap to azelaic acid or a peptide serum.
Build my routine to see where this fits.
S
salicylic acid
PMActiveAn oil-soluble acid that clears inside the pore rather than only on the surface. Best for congestion and blackheads.
Pregnancy Leave-on strengths above 2% are usually avoided; a rinse-off cleanser is generally considered fine.
Also called: bha, beta hydroxy acid, salicylic
Build my routine to see where this fits.
skin cycling
PMMethodAlternating active nights with recovery nights so skin gets the benefit without the irritation.
Build my routine to see where this fits.
slugging
PMMethodSealing a finished night routine under a thin occlusive layer. Excellent for dry skin, risky over actives.
Build my routine to see where this fits.
spf
AMSun careHow much longer skin resists burning. SPF 30 or higher, applied every morning, does the bulk of anti-ageing work.
Also called: sun protection factor, sunscreen
Build my routine to see where this fits.
squalane
EitherBarrierA light, stable oil that softens skin and slows water loss without feeling heavy or clogging pores.
Build my routine to see where this fits.
T
tewl
JargonTransepidermal water loss — water evaporating out through the skin. High TEWL is what tightness and flaking feel like.
Also called: transepidermal water loss
Build my routine to see where this fits.
tranexamic acid
EitherActiveTargets stubborn discolouration and melasma without exfoliating. Pairs well with niacinamide.
Build my routine to see where this fits.
U
urea
EitherHydratorBoth a humectant and a mild softener. At 5–10% it smooths rough, flaky patches without acid sting.
Build my routine to see where this fits.
V
vitamin c
AMActiveA morning antioxidant that evens tone and supports SPF. Look for a stable formula in an opaque bottle.
Also called: ascorbic acid, l-ascorbic acid, ascorbyl glucoside
Build my routine to see where this fits.
W
white cast
AMSun careThe grey film some mineral sunscreens leave on deeper skin tones. Tinted or chemical filters avoid it.
Build my routine to see where this fits.
Z
zinc oxide
AMSun careA mineral UV filter that sits on the surface and covers the full UVA/UVB range. The usual pick for reactive skin.
Also called: mineral filter, titanium dioxide
Build my routine to see where this fits.
How to read an ingredient list
Ingredients are listed by weight, highest first, until you reach 1% — after that the order is the brand's choice. So water, glycerin and the base emollients sit at the top of almost everything, and the active you paid for often sits in the back half of the list beside the preservatives. That is normal: most actives work at low percentages.
What matters more than position is whether the formula suits the job. A well-buffered 5% acid will beat a badly formulated 10% every time, and a hydrating serum with nothing but humectants still needs a moisturizer over it to hold the water in.

Where these words show up next
- In your routine: every step card has a “Look up an ingredient” search, opened on the terms that step actually uses.
- In the order guide: the AM and PM sequence shows where each category belongs and how long to wait between layers.
- In the pairing checker: two ingredients at a time, with the verdict, the order and the wait.

