Can we reuse last summer's sunscreen?

Like all skincare products, sunscreen should have a Period After Opening (PAO) indicated on its label, which is the maximum duration the consumer can use the product after it has been opened. This period, usually determined by the manufacturers, is represented in the form of an open jar and typically falls between 9 and 12 months after its first use, beyond which its photoprotective properties are no longer guaranteed. This is particularly related to the conditions of use and storage of the product once opened, to which UV filters are sensitive. However, there is no conclusive data to determine whether it is safe or dangerous to use sunscreens beyond the PAO specified by the manufacturer.

Whether left on the sand or by the poolside under direct sunlight, forgotten inside the car, or stored at 4°C in the cargo hold of an airplane, it's not uncommon for our sunscreens to be exposed to extreme temperatures. However, these exposures to varying temperatures can have an effect on the stability of the chemical constituents and lead to irreversible alterations of the physical characteristics of sunscreens: phase separation and discoloration of the emulsion, effects that can become more pronounced after exposures to warmer temperatures.

However, these changes can result in a decrease in the effectiveness of sunscreens to protect the skin by reflecting and/or absorbing UV rays, and thus indirectly pose a danger to the skin. Disturbed, the sun filters therefore degrade over time and their effectiveness is reduced.

Recommendation : Education on preventing damage induced by UV rays also includes proper storage of sunscreens to ensure the integrity of their sun protection potential. To avoid any potential damage, it is recommended to store them away from heat and direct sunlight, in a dry and cool place. However, if the sunscreen has been subjected to extreme temperatures and physical changes are visible (discoloration, phase separation), it is preferable to opt for a new sunscreen. Moreover, once the PAO (Period After Opening) has passed, it is better to change your sunscreen, even if it still looks good visually.