Hand on heart: when did you last change your sheets?

So: when did you last change your bed linen? And we'd like the real answer, please, not the one you'd give your mother-in-law.

Ask that at a cosy dinner and the answers will range from "every Sunday, obviously" to a very long silence and a "Why, can you tell?". We'll just leave that there.

What shares the bed with us

We spend around a third of our lives in bed, and in that time we leave quite a lot behind: skin flakes, hair, moisture, traces of face cream, make-up and hairspray. And because we sweat at night, even when we don't notice, the bed is warm and a little damp.

One group is especially delighted about that: house dust mites. You can't see these tiny flatmates, but they love exactly this climate and live on our skin flakes. For allergy sufferers that's no joke, and for everyone else it's not a lovely thought to fall asleep to.

How often is often enough?

There's no fixed rule, but there's a good rule of thumb. Pillowcases can go in the wash every week, because that's where your face lies and where cream and hair end up. Duvet covers and sheets every one to two weeks, and more often in summer, when you've got a cold or when the dog shares your bed. The duvet and pillows themselves just need airing regularly and cleaning now and then, with down best done the way the maker recommends.

Which leaves the mattress. It really won't fit in the washing machine, and that's exactly what a mattress protector is for: it can be washed and protects what's underneath.

The best feeling of the week

And between you and me: is there anything nicer than slipping into a freshly made bed at night? That cool, smooth feeling on your skin, the smell of clean laundry, everything feels like a fresh start. To me it's one of the most affordable luxuries there is.

A small tip: keep two sets of linen for every bed. Then you can put fresh sheets on straight away, and "the other set's still in the wash" no longer counts.

So fresh bed linen is less a chore from your grandmother's housekeeping book than a small gift to yourself, as often as you can manage.

And if you had to do a quick bit of maths while reading this: tonight would be an excellent time.