Can we reuse last summer's sunscreen?

Like all skincare products, sun cream should display a period after opening (PAO) 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 between 9 and 12 months after its first use, beyond which their photoprotective property is no longer guaranteed. It 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, abandoned inside a car, or stored at 4°C in an airplane's hold, it's not uncommon to see our sunscreens exposed to extreme temperatures. However, these exposures to varying temperatures can have an effect on the stability of the chemical constituents and cause irreversible alterations to the physical characteristics of sunscreens: phase separation and discolouration of the emulsion, effects that can become more pronounced after exposure to warmer temperatures.

However, these changes can result in a reduction 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 become degraded over time and their effectiveness reduced.

Recommendation : Education on the prevention of UV-induced damage also includes the correct 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 (discolouration, phase separation), it is preferable to opt for a new sunscreen. Furthermore, once the PAO (Period After Opening) has been exceeded, it is better to change your sunscreen, even if it still looks visually good.