"You should not use expired sunscreen because it becomes less effective," Madan told Good Housekeeping . "This leads to less protection, which means more sunburns, increased risk of skin cancer, and increase in sun damage."
According to Senior Chemist Sabina Wizemann of the Good Housekeeping Institute, the quality of the formula itself degrades with time.
"Once the emulsion is compromised, the product may not spread well, become thinner, and may not be able to attain its original viscosity needed to coat the skin evenly," she tells Men's Health.
How long does sunscreen last?
Generally, sunscreens are designed to last up to three years if stored under manufacturer's recommendations. But it's easy to forget when we purchased that bottle of Banana Boat and whether we left it in the sun for hours on end.
"Most of us forget about sunscreens (especially body sunscreens) and toss them into our garages or cars once the beach days are over not knowing for sure if these rooms get too cold or hot to compromise the product's effectiveness," says Wizemann.
Color and consistency changes can indicate that your SPF have turned, but Wizeman recommends starting fresh with a new bottle every summer.
"This way, the second-guessing of the formula's safety, efficacy, and cosmetic aesthetic properties are taken out of the equation," she says.