Recording the expiration date and opening date of cosmetics is more important for skin health than you might think.

If you frequently get small, unexplained breakouts despite switching between various cosmetics, I recommend checking when the products you are currently using were opened. I once had a bad reaction myself after trying to save an essence that had been open for over a year because I didn't want to waste it. Since then, I make it a point to write the opening date on the container with a permanent marker whenever I open a new product. Jar-type creams that don't use a spatula, or gentle natural skincare products, spoil faster than expected, so managing expiration dates seems to be just as fundamental to home care as regularly washing your bedding.