Basic hygiene, really: you don’t want an eye infection. Whatever make-up you are sharing, you’ll be sharing all the bacteria that’s on it too. Over to Ashley Ward, Max Factor Make-Up Artist: “Sharing mascara is a big no-no. I would never use the same wand on different people because of the possibility of spreading infection. As a basic rule of beauty hygiene, I would recommend replacing mascara every four to six weeks.”