It's the day before your holiday, you've semi-packed (aka, emptied the entire contents of your wardrobe onto the bed) and then it hits you. Sun cream. Last year's holiday left you with a ton of half-full bottles, and they're all sitting there in that cupboard under your bathroom sink.
Question is, how do you know if they've gone bad?
We hit up cosmetic dermatologist, Dr Mervyn Patterson from , to find out - once and for all - what's the deal with sun cream going bad? How long does it last? And most importantly, how do you know if it's expired?
Let's go back to the basics...
Firstly, does sun cream expire?
'Most sunscreens do expire and because of this a lot should come with an expiry date stamped on the box,' explained Dr Patterson. 'It is very important not to ignore this as the chemicals do degrade and may well lose their protective effect.'
That's all well and good, but what if you've thrown away the box - and with it - the expiration date? As a rule of thumb, Dr Patterson says most sun tan lotions will last for 'at least a year of use'.
How to tell if it's gone bad...
The warning signs to look for, are smell and texture. If your sun protection has expired the formula will have 'started to separate'. 'If it's looking different in terms of texture or smell from when you first bought it, then things may not be well with the product. In this case, it's best to simply discard.'
What happens if you use expired sun cream by accident?
Short version? It's pretty likely you'll burn and the formula itself could trigger a reaction from your skin. 'If a sunscreen product has deteriorated, then in theory there is a risk of chemical alteration of the ingredients.' And what does this mean? Well, there's a greater likelihood of 'contact reactions' with the skin, which means it could be irritating. There will also be a 'fall in sun protection', hence the burning. Ouch.
So what causes it expire? These are the triggers to avoid...
Most sun creams have been designed to withstand a lot, 'however if the containers are left in direct sunlight even the most stable of formulations can degrade.' Dr Patterson continues, 'storage is important. Leaving your sunscreen baking in the sun, whether it's on the beach, or in the back window of your car, may trigger degradation of the formula, and that renders the product useless.' The best place to store it? Somewhere shaded, preferably cool and dry.
So now we know what to do (and what not to do) to give our SPF the longest life possible... Just remember, if in doubt chuck the old stuff and pick up a new bottle - we know sun cream can be pretty pricey, but it's worth protecting your skin no matter what.