My personal skin care method: Observe the expiration date. The clock on cosmetics starts ticking the moment you open it.

The number written on the bottom of the cosmetic product is only the expiration date when unopened.
The moment you open the lid, air and moisture enter, and oxidation of the ingredients begins.
Essence that has been left in the corner of the vanity for over a year because it is a waste is no longer a nutrient for the skin, but rather a chemical toxin.
From today onwards, please write the opening date in large letters on the lid of the product instead of the bottom with a permanent marker.
The golden time for basic products is 6 months to 1 year. no see.
The most expensive skin care routine begins with discarding products that have lost their freshness.