my mum and my sister both insist on every week and I reckon it makes sense when you think of how much two people sweat each night. I usually manage every fortnight and feel a bit scummy about it. But I know plenty of people who think it's ok to wait a month. DH would wait until there were things crawling around and the sheets could stand up on their own. I change DS's cot sheets and sleeping bag once per week as I think that's a bit different. So, what do you all do?