An innocent patch test meant Judy Johnson avoided one of her worst ever skin reactions being on her face - but is it all a numbers game?

Any products in this article have been selected editorially however if you buy something we mention, we may earn commission

In my limited experience of such things, I’m starting to think that looking after your skin is a lot like looking after a baby. Give it what it needs, and it’s all smiles, glowing and happy and rewarding you with peace and quiet. Fail to give it what it needs, and you’re left with something that is, metaphorically, screaming at you to sort it out without quite telling you what will do the job. 

That was how I felt, anyway, when I recently patch-tested an essential oil-filled serum  on the inside of my arm and was left, three days later, with one of the worst reactions of my life. There were definitely moments of me yelling at said arm ‘WHAT DO YOU WANT FROM ME?!’, desperately trying everything and anything to calm it down before resigning and letting it run its course in the hope it would soon exhaust itself. It did... five weeks later. 

All this was in the hope of testing out a facial that used the same product, so in fairness it could have been far worse (as I repeatedly told my appalled friends and colleagues, who kept asking whether perhaps I should seek some medical help for the intense rash that was growing across my arm). It could have been my face.

MORE GLOSS: 20 irritating truths of living with sensitive skin

This fact, coupled with the way it happened, gave me a newfound firm appreciation of patch testing; I mention it in almost every column , but it’s only now that I realise dotting something on my neck 24 hours before using it all over my face is not enough. This reaction happened after three consecutive days of testing; the first two days caused no problems whatsoever, giving me false hope that the facial would do me and my skin the world of good. 

Then comes day three, when I absent-mindedly tested my third dose of serum after a shower, innocently assuming it’d sink in without trouble - and within seconds, I knew something was wrong. Little red bumps appeared,  itchy and burning, so I quickly washed it off and applied my topical steroid cream from the GP. 

But within a matter of hours it had spread, big, blotchy and angry, spreading to around 10cms in diameter with raised red bumps that looked a little like a bad nettle rash. I tried more steroid cream; it just felt hotter. I tried calamine cream; it just made it sticky and therefore more uncomfortable. I tried my failsafe rosehip oil; it did nothing. Taking on a life of its own, it quickly got worse before it got better a long, painful, embarrassing five weeks later (including a trip to the doctors, more steroid cream and so many antihistamines I’m surprised I stayed awake). My GP advised that this was an allergic reaction, not simply a sensitivity - but I've no idea which ingredient caused it. As is so often the case, this is why testing new products out thoroughly is so vital.

So why was day three such a turning point? "A topical reaction will often be evident after 24 hours, but I would recommend not washing the area for 48 hours,” Content Beauty’s  founder and skincare expert Imelda Burke  tells me. "Testing over several days in the same area is a good idea as some effects may be accumulative. It is possible to become sensitive to an ingredient after prolonged use.”

This makes sense - I’ve used shower gels before which have been fine for a week or two and then slowly caused skin issues with continued use; but does the condition of your skin make a difference too? "Skin is slightly more absorbable when warm, such as after a shower,” says Imelda, convincing me that that may have been what was necessary for my reaction to take off. It's worth testing on thinner areas of the skin, too; inner arms at the elbow, wrists or behind the ear will give you a better idea of how something will perform on your face.

Imelda continues, "A test may not be accurate if you have been using a steroid cream on the area or taking anti-inflammatory medication. It is best not to patch test when you know you will be working out or in humid hot weather too – sweating may affect the results. Keep the area as dry as possible during the test and avoid sunlight.” Helpful, then, that we had one of the hottest Septembers ever at the time that my skin decided to play up. 

Of course, a simple patch test at home is only handy if you are fairly on top of your arch enemies already . Every new product I try goes through a (now more thorough) patch test but ideally, if you’re often sensitive or reacting to skincare a professional test is what you need. They’re hard to get unless you have a sympathetic GP, but well worth the wait.

MORE GLOSS: What to have in your cupboard in case of skin reaction emergencies

“Your GP will refer you to an allergy clinic to have tests performed for common chemicals or substances known to cause allergies. This can be everything from cosmetic ingredients to things like rubber and nickel,” explains Imelda. "Each substance is then applied to a disc and taped to the back or the inside of the arm and left for 48 hours. The patches are then removed and checked for redness and irritability. The area is then assessed after a further two days.”

Time, then, really does tell; if even the doctors are playing the waiting game then we amateurs would be best advised to play it too. The inside of your arm and behind your ear are your new testing ground; use them to avoid skin tantrums elsewhere and the rest should be plain sailing.

Struggling with your sensitive skin?  Download my Beginner's Guide to Sensitive Skin  now for 25 pages of expert advice, skin care routines, product recommendations and more