Suncream manufacturers say you should buy new stuff every year, as the previous year’s cream loses its effectiveness. True? Or just a marketing scam to keep up sales?
This is actually true. There are two types of suncream, some with zinc particles and others than contain other chemicals. The non-zinc based suncreams are the most commonly available ones; they absorb into the skin and don’t leave a thick white layer behind. The chemicals in these creams are quite unstable, and are broken down by exposure to sunlight (in this way, the suncream absorbs the radiation, instead of your skin.) This also means that they will break down over time, and last year’s cream will not be as good at protecting you from the sun as a new batch would.