Unlike fine wine, cheese and George Clooney, make-up does not improve with age. You probably know you should spring-clean your make-up bag every so often, but do you bother to do so? If you wait until your favourite foundation could ice a cake before replacing it, then take note: make-up goes off. Some products stay fresh longer than others, but they go off none the less. Given that you wouldn't eat rotten food, why put rotten make-up on your face?

You should overhaul your make-up bag at least twice a year, but also check individual products when you use them. Handily, all make-up smells much the same once it goes off, so the minute something starts to acquire even a slightly musty, mouldy or rancid air, bin it.

The biggest culprits are the products you dip your fingers into: foundation, lip glosses and the like will always have the shortest shelf life; and, unless you use them frequently, they will probably need replacing before they run out. Anything with an applicator or a pump action, meanwhile, tends to last longer.

Some say mascara can last up to six months, making it more likely to dry up before it goes off, but if you've had yours any longer than that it's a fairly safe bet there's bacteria growing inside the barrel. Nice. And it's no good having squeaky clean make-up if your brushes are filthy. "Wash your brushes whenever they look dirty," says Lisa Eldridge, make-up expert for Boots' new Pure Beauty stores. "Don't bother with astringent cleaners, instead use a conditioning shampoo or a two-in-one shampoo, which will leave the brushes nice and soft. Wash them, rinse them well and dry on a flat surface."

If the thought of creepy-crawlies feasting on your favourite lipstick doesn't inspire you to have a regular spring-clean, Eldridge has a fantastic tip: "You can wash your old make-up bag, but I find buying a new one gives me a great incentive to keep everything in it clean. If you start with a new bag, it's amazing how ruthless you are."