Toss it: Every 3 months
The reason: In order to prevent an eye infection (bacteria love to hide away in these pretty tubes), replace your mascara four times a year. Plus, by three months your mascara will likely be dried up and cakey anyway. When you're applying mascara pumping the tube can cause it to dry out faster, instead twirl the brush inside to decrease the amount of air that gets in.
Photo Credit: Getty Images/Davies and Starr