Niacinamide, also known as vitamin B3, is a stable compound that has a relatively long shelf life. When stored properly, it can remain effective for up to two years. However, it is important to note that the efficacy of any skincare product, including niacinamide, can be influenced by various factors such as exposure to light, air, heat, and contaminants. To maximize the shelf life of niacinamide, it is recommended to store it in a cool, dark place, away from direct sunlight and extreme temperatures. Additionally, ensuring the product is properly sealed after each use can help maintain its efficacy for longer. Always check the expiration date on the packaging and discontinue use if the product has expired or shows signs of degradation, such as changes in color, texture, or smell.