[Medical Q&A] How long does it take for sunscreen to become invalid after it is opened?

Planner: Chinese Medical Association

Reviewer: Yang Weiling, Chief Physician, General Hospital of Rocket Force of the Chinese People's Liberation Army

The shelf life on the cosmetic packaging usually refers to the storage time of the product when it is unopened. Most cosmetics have a shelf life of 3 years. However, once it is opened, the situation is different. It is recommended to use up opened cosmetics, especially sunscreen, within 6 to 12 months. This means that if you have a bottle of sunscreen purchased last year, if it has not been opened, you can continue to use it safely; but if it has been opened, even if it has not exceeded the shelf life marked on the package, the sunscreen ingredients may become oxidized and ineffective due to long-term exposure to the air.

The "6M" or "12M" logo commonly seen on sunscreen packaging means that it should be used up within 6 months or 12 months after opening. The shelf life of sunscreen varies from brand to brand and formula to formula, so it is best to use it up within the recommended time. An important tip about the amount of sunscreen to use is: the amount used on the face should not be less than 1 ml each time. Taking a 30 ml bottle of sunscreen as an example, if used correctly every day, theoretically it should be used up within a month. If you find that a quarter of the sunscreen has not been used up, you may want to check whether you have applied enough each time before worrying about the shelf life.