This is a question that is often asked about cosmetics and other products that have a shelf life. The answer, unfortunately, is not always clear cut. In general, most products will last for at least a year after being opened, but there are exceptions. For example, products that contain natural ingredients or that are meant to be used within a certain time frame may not last as long. Additionally, storage conditions (such as temperature and light exposure) can affect a product's shelf life.
If you're unsure about how long a particular product will last, it's always best to check the label or contact the manufacturer. They will be able to give you more specific information about the product in question.