Patch Test Like a Pro

What are “actives”?

An active is an ingredient that does something specific beyond cleansing and moisturising. They’re the exciting part of skincare, and also where most irritation comes from.

Active	What it’s for	Good to know
AHAs (glycolic, lactic, mandelic acid)	Exfoliate the surface for smoother, brighter skin	Can sting; increase sun sensitivity
BHA (salicylic acid)	Gets inside pores; great for blackheads and breakouts	Oil-soluble, handy for oily skin and razor bumps
Retinoids (retinol, retinal, adapalene)	Long-term texture, breakouts and signs of ageing	Start low and slow - 2 nights a week
Vitamin C	Antioxidant; brightens and helps fade dark marks	Best in the morning under SPF
Niacinamide	Calms redness, helps oil control and the barrier	Usually very gentle, a great first active
Azelaic acid	Redness, bumps and dark marks	Gentle-ish multitasker
Benzoyl peroxide	Breakouts	Can bleach towels and pillowcases!

Some combos to keep apart (at first)

• Retinoids + strong acids (AHA/BHA) on the same night → often too irritating. Use on alternate nights.
• Benzoyl peroxide + retinol at the same time → can deactivate some retinoids and irritate.
• Lots of actives at once → the most common way people wreck their skin barrier. If skin suddenly stings, gets tight, shiny-but-flaky or red, stop the actives and go back to cleanser, moisturiser and SPF until it settles.

The patch test, step by step

1. Choose a spot. The inner forearm is easiest. For face products, many dermatologists suggest a spot that reacts more like facial skin - behind the ear or a small patch along the jawline.
2. Apply a small amount twice a day, just as you would normally use it, to the same spot.
3. Do this for 7–10 days. Some reactions take days to show up.
4. Check daily for redness, itching, swelling, burning or little bumps.
5. No reaction? Lovely - you can start using it as directed. (Patch testing lowers the risk but can’t guarantee you’ll never react.)
6. Reaction? Wash it off and stop using it.