If you’ve stuck with one brand for years, sure. When you sweat, your armpits harbour smelly bacteria, and just as bacteria can become resistant to antibiotics, it’s possible your pits have become immune to the ingredients in your deodorant. “It’s a good idea to switch up your deodorant brand every six months to prevent resistance,” says Dr Han Lee, an assistant professor of dermatology at the University of Southern California. You can also fight the stink by cutting off bacteria’s food supply: Sweat. “Antiperspirants obstruct the sweat ducts, reducing the amount of substrate for bacteria to act on, hence reducing odour,” says Dr Derrick Aw, a consultant dermatologist from the department of medicine at the National University Hospital. For a protective benefit, choose one that has about 20 per cent aluminium chloride, says Dr Aw.