The shelf life of Retinol Serum depends on various factors, such as the type of packaging and storage. Generally, the shelf life of Retinol Serum after opening is 6 to 12 months if stored in a dark and cool environment. It is important to check the jar symbol on the packaging, which indicates how long the serum can be used after opening, and not to use the serum if it has expired or smells or looks unusual.