Sunscreen is supposed to protect you from UV rays, but can sometimes be dangerous. Manufacturers guarantee the effectiveness of the sunscreen until the specified best-before date.
The fact that the sunscreen no longer provides sufficient protection is due to the oxygen that gets into packages that have already been opened. It is better to dispose of sunscreens from the previous year if they have been frequently exposed to high heat, such as in the beach bag or in the car – even if the best- before date has not yet passed.