I have a spray sun protector, on it is a date that the product is good until 12 months after opening. However, there is no shelf date. Since it's a spray it has not been in contact with the outside environment, so why would it spoil? Should I continue using it? In other words, should I not accept the product claim that it expires 12 months after opening? I can exchange it for a cheap brand for 70% off, but it feels like a waste to throw the bottle away.