A half-full bottle of sunscreen is hidden in the bathroom cabinet. Is it just what you need to protect your skin from UV rays during the first few days of strong spring sunshine? Rather not. With old sunscreen there is a risk that it no longer offers sufficient protection.
Consumers can usually find out how long the sunscreen can be used after opening on the packaging. There should be an open jar on the bottle that says “12 M” for example. The sunscreen can therefore be used for a maximum of 12 months after opening. Only up to this point does the manufacturer guarantee undiminished effectiveness. If stored incorrectly, the sunscreen can lose its effectiveness more quickly, for example if it has been exposed to great heat or has been in a warm car for a long time.
The dermatologist Professor Eckhard Breitbart basically advises buying a new pack instead of using an old sunscreen. He explains to the “Apotheken Umschau”: If the sunscreen bottle is open, oxygen enters. The oxygen leads to oxidation and this process means that the ingredients change and the protective function can no longer be properly maintained.
Researchers from the Sorbonne and scientists from the national research authority CNRS showed in a study in 2021 that sunscreen with the chemical UV filter octocrylene has another problem if it is stored for a longer period of time. The molecule benzophenone develops in the creams over a period of one year – it is considered to be possibly carcinogenic. The substance can also cause allergies.
The researchers examined 17 sunscreens with an SPF of 50. 16 contained octocrylene. The scientists placed the sunscreens in an incubator for six weeks. It was 40 degrees warm inside and the humidity was 75 percent. After these six weeks, the creams were in the same condition as they would have been after one year of storage at room temperature. The researchers did not find any benzophenone in the sunscreen that did not contain octocrylene. With the other 16 sunscreens, the scientists found 39 mg/kg benzophenone even when fresh. After the six weeks, the concentration almost doubled to 75 mg/kg.
According to the NRW consumer advice center, mineral UV filters such as “Titanium Dioxide” or “Zinc Oxide” are generally more stable and the creams can be used longer. Consumers can tell whether a sunscreen contains octocrylene by looking at the ingredients. It says there: “Octocrylene”.
Sources: Sorbonne study, Apotheken Umschau, NRW consumer advice center
