If you're anything like us, you hoard your knickers until there are literal holes in them. Well, according to research, that is definitely not the most healthy or hygienic practice. They are items we (hopefully) use every day and (hopefully) couldn't live without them, so it really shouldn't come as a surprise that they need to be replaced frequently. Underwear needs to be replaced at least once a year, according to Professor of Environmental Health at the University of Salford, Dr. Lisa Ackerly. When it comes to daily use, a pair of underwear should last ONE day only. No excuses. You may think this is a no brainer, but a whopping one quarter of males and seven per cent of women get two days out of a pair, according to a Kelkoo survey. Dr. Lisa told the Irish Mirror that used underwear contains microbes that can cause urinary tract infections, pneumonia and blood infections, as well as E-coli and thrush. She advises to change "after every single wear – no exceptions" and "replace them every year.” When it comes to washing your smalls, Professor Sally Bloomfield, Consultant in Hygiene and Infectious Disease Prevention advises a machine wash at 30-40C using a detergent with an AOB (activated oxygen bleach) product. Although, if someone in the family is ill, she recommends a 60C wash and an antibacterial product thrown in.