The Ecological Transition Agency (ETA) has come out with clear guidelines on how often you should wash pieces of clothing.

The ETA says you should wash a pair of jeans 30 times before chucking them in the wash.

Bras should be worn seven days, t-shirts five days, and sweaty sports clothes at least three times.

Lulu O’Connor, founder of The Clothes Doctor, a luxury clothes-cleaning business, believes more people should spot-wash certain items.

“People do over-wash,” O’Connor told The Times.

“People are lazy about looking after clothes and throw them in the wash every time they’ve worn them because, frankly, it’s easier than steaming or spot cleaning or hanging them up.”

O’Connor said that her customer guidelines are “very similar” to the ETA’s.

She tells customers that sheets and pyjamas get washed once a week, while bras get washed every three or four wears.

With t-shirts, a wash every five days is plenty, but more frequently in the summer.

“But denim and knitwear don’t need much washing at all. We say 30 wears for jeans, 15 wears for jumpers.”