Patch testing is the single cheapest insurance policy in skincare. Two minutes of effort and a day or two of patience can save you a week of red, flaking, irritated skin, and it's the only reliable way to know how your skin will react to a new product before you put it on your face.
We always recommend a patch test when you start a new product, even if the ingredients look similar to something you already use. Formulas differ in concentration, pH and preservatives, and any one of those can be the thing your skin objects to. Better safe than sorry.
Which products should you always patch test?
Technically all of them, but realistically these deserve it most:
- Exfoliating acids (AHAs like glycolic, BHAs like salicylic)
- Retinoids (retinol, retinal, tretinoin)
- Vitamin C serums, especially L-ascorbic acid formulas
- Anything heavily fragranced or containing essential oils
- Any product if you have sensitive or reactive skin, eczema or a history of allergies
Step 1: Apply the product to an inconspicuous area
Pick a patch of skin that's out of the way in case things go wrong. The inner forearm or inner elbow is the classic choice: the skin there is thin enough to be a reasonable stand-in for facial skin, and easy to keep an eye on. The area behind the ear or the side of the neck works too, and is slightly closer to facial skin if you want a stricter test.
Apply a small amount, roughly the size of a 5p coin, to clean, dry skin.
Step 2: Cover the area
Not everyone bothers with this step, but it makes the test more reliable. Covering the spot with a plaster or small bandage keeps the product from rubbing off on clothes and stops it spreading beyond the test area, so if a reaction does happen, you know exactly what caused it and where.
One exception: don't occlude exfoliating acids or retinoids under a plaster for the full duration, as trapping them against the skin intensifies them beyond normal use. For those, an uncovered test on the inner arm is fine.
Step 3: Wait 24 to 48 hours
The least fun step. Most irritation reactions show within 24 hours, but true allergic reactions can take up to 48 hours or occasionally longer to appear, so give it two full days if you can. Check the area once or twice along the way.
A small amount of transient tingling or mild redness is normal with exfoliating serums. What isn't normal:
- Persistent redness or itchiness
- Small red bumps or hives
- Flaking or peeling
- Swelling, burning or stinging that doesn't settle
Any of those means the product isn't compatible with your skin. Wash the area with a gentle cleanser and discontinue use.
Step 4 (optional but smart): test near the face
If the arm test passes and the product contains strong actives, do one final short test on a small area at the jawline or behind the ear for a night or two before applying it all over your face. Facial skin is more reactive than arm skin, and this catches the borderline cases.
What to do if you react
Stop using the product, keep the routine minimal (gentle cleanser, plain moisturiser, SPF) and let the skin settle. If your barrier feels wrecked, our skin barrier repair guide walks through recovery step by step. For severe reactions, swelling, or anything spreading beyond the application site, see a pharmacist or GP.
That's all there is to it. A couple of days of patience and you'll know for certain whether a product deserves a place in your routine.
FAQs
How long should you patch test skincare?
48 hours is the gold standard. Irritation usually shows within 24 hours, but allergic reactions can take up to two days to develop. If you're impatient, 24 hours catches most problems; just keep an eye on the area for the following day too.
Does tingling mean a product is working?
Not really. A brief tingle from an exfoliating acid or vitamin C serum on first use is normal and settles within a minute or two. Tingling that builds, burns or comes with redness is irritation, not efficacy. "It stings, so it's working" is a myth that keeps a lot of people using products their skin hates.
Do I really need to patch test everything?
Realistically, no. A basic moisturiser or cleanser from a brand you already use well is low risk. The non-negotiables are strong actives (acids, retinoids, vitamin C), anything fragranced, and every new product if your skin is sensitive or you've reacted to things before.
Can I patch test more than one product at once?
Yes, if you keep them apart and keep track: one product per forearm, or clearly separated spots. What you shouldn't do is introduce several new products to your face in the same week, because if a reaction appears you won't know which one caused it.