How often do you change your sheets? According to New York microbiologist Phillip Tierno, for two-thirds of us, the answer is "not often enough".
According to a YouGov poll, only a third of us changes our sheets once a week, as Tierno recommends. 30% of us bundle the bedclothes into the washing machine every fortnight, while one in ten of us only bothers once a month. But is a week or two here or there really such a big deal?
Let's consider the facts - but unfortunately, they don't make for easy reading. You produce around 26 gallons of sweat in bed each year, helping to cultivate an environment described by scientists as an "ideal fungal culture medium". Samples of feather and synthetic pillows between 18 months and 20 years old indicate that a single pillow can contain up to 16 species of fungus.
This combines with the bacteria contained in your sweat, saliva, mucus and other bodily excretions to produce a veritable "botanical park" of bacteria and fungus - nice. Sleeping with the window open won't help much, either: you sweat all year round.
And don't forget the lint, dust mite debris and faeces you are "almost forced to breathe in" each night - on average, you can expect to share your bed with 10 million dust mites. Exposure to these materials can trigger sniffing and sneezing, Tierno explains: "Even if you don't have allergies per se, you can have an allergic response". Reason enough to make today laundry day, no?
According to microbiologist Laura Bowater, we should be washing our sheets at a minimum temperature of 60°C in order to kill off bacteria. "Dry sheets and pillowcases in direct sunlight if you can, as UV light is effective in killing micro-organisms," she recommends. "Run a hot iron over pillowcases on the cotton setting (200°C) to kill any leftover bacteria."
You should also aim to clean your mattress at least twice a year. First, strip and wash your bedding. Before you put it back on, open the windows to air your mattress. Vacuum the mattress thoroughly, using a handheld vacuum or vacuum with a clean brush attachment, paying special attention to seams and crevices.
Sprinkle with baking soda to eradicate any nasty odours, before leaving it to air for another hour or so. Vacuum again to remove all traces of baking soda, then leave it to air for a little longer before putting the sheets back on.