The World Health Organization has Five Moments for washing hands: 1  before patient care. 2  after environmental contact. 3  after exposure to blood/body fluids. 4  before an aseptic task, and. 5  after patient care.
This means that you can use leftover sunscreen from one year to the next. Some sunscreens include an expiration date â a date indicating when they're no longer effective. Discard sunscreen that is past its expiration date. If you buy sunscreen that doesn't have an expiration date, write the date of purchase on the bottle and be sure to throw it out within three years. Also, discard sunscreen that has any obvious changes in color or consistency.
He also recommends that every year, throw out last years sunscreen and use new. It's safe to use sunscreen and such after the expiration date (unless it smells funny or such (this also applies before the expiration date)), it's just that it might not be as effective in protecting you against the sun.