Every morning you diligently apply SPF and pack a bottle of sunscreen when you know you’re going to be out all day, but chances are you’re not reapplying as frequently as you should. “People think that buying a high SPF will allow them to put it on once and leave it on, but that’s not true,” explains Anastasia Ivanova, Campaign Manager for La Roche-Posay’s MySkinCheck. “Regardless of the SPF, you need to reapply every two hours.” Dr. Sandy Skotnicki, Medical Director of the Bay Dermatology Centre agrees, “You need to reapply every two hours as the chemical sunscreens break down in the sun.”

For casual exposures, say running a couple errands outside or going to work, newer technologies in sunscreens such as Neutrogena, La Roche-Posay and Ombrelle, will last eight hours, assuming you aren’t jumping in the water or excessively sweating. “A good habit to get into is to apply a bit of sunscreen to the arms, chest and face before you dress in the morning,” says Dr. Skotnicki. “I would not worry about reapplying in these cases, unless you’re high risk, which means, fair skin, freckles, over 50 moles or a family history of skin cancer.”

Swimming or sweating up a storm? Even if you’re using a sunscreen that has a “water-resistant” or “sweat-proof” label, you need to reapply shortly after. “Water-resistant means it retains its SPF 45 minutes after bathing,” says Ivanova. “You won’t lose it right when you go in the water, but after that it will deteriorate, so you need to reapply.”