If in doubt, don’t rub yourself in with the sunscreen you’ve used from last summer. That’s what dermatologist Professor Eckhard Breitbart advises.
Instead, it is better to buy a new tube in the supermarket or in the drugstore.
Because oxygen leads to oxidation and this process means that the ingredients change and the protective function can no longer be maintained correctly, says the expert from the German Cancer Aid and Chairman of the Working Group on Dermatological Prevention (ADP) about his advice.
In addition: “Substances that can arise in the process could well be carcinogenic,” says Breitbart. Although the “correct proof” has not yet been provided.
A study by French and American scientists, published in March 2021, has provided new evidence for the thesis: According to this, benzophenones, which are considered possibly carcinogenic, have formed over time in creams with the UV protection filter octocrylene.
Observe the information on the tube
The maximum length of time you should use a sunscreen after opening is written on the tube or the jar: The corresponding symbol is an open round jar with the information “12 M” on it, for example.
That means twelve months. After that they should be disposed of.
In order not to lose track of exactly when you opened a sunscreen, it is advisable to write the date of opening on the tube with a waterproof felt pen.
Why there is often no use-by date
In addition, sun creams sometimes, but by no means always, have a best-before date. If this is exceeded, they should also no longer be used, advises Breitbart – even if they are still unopened.
Manufacturer Nivea writes, for example, that sun protection products can be kept for at least 30 months from the date of manufacture when stored in a cool and dry place – this applies equally to sprays and creams.
The manufacturer advises: discard the cream if it smells acrid or unusual, has changed consistency, has become oily or watery, or if the contents are discolored.
Apply sunscreen liberally
With regard to the selection of the cream, dermatologist Breitbart advises using perfume- and fragrance-free products and making sure that they protect against UVA and UVB rays.
When using the protective agent, thrift is inappropriate. The products only provide the promised sun protection factor if they are applied sufficiently thickly to the skin.
“A rule of thumb is: A heaped teaspoon is needed for the face alone for adolescents – for adults a little more,” says the doctor.
He also points out that sunscreen alone is not the perfect way to keep the risk of skin cancer low.
These are sun protection clothing and avoiding the sun when there is high UV exposure, for example during lunchtime.
Jeans as a UV protection shield
With regard to clothing, it should be noted that it offers very different levels of UV protection. The sun protection factor of dark blue jeans is around 500, while a thin white cotton T-shirt only has 10, explains dermatologist Sebastian Singer in the magazine ‘Apotheken Umschau’.
If precise UV protection values are important to you, you can of course fall back on UV protective clothing. According to the report, however, their textile sun protection factor is reduced by frequent washing.
And if you generally go swimming with clothes on, you should consider: Wet clothes offer less protection in comparison.
Danger of sunburn despite clouds
A deceptive assumption is that clouds make UV protection superfluous, explains the German Cancer Aid. In fact, clouds affect the level of UV radiation in different ways: while thunderclouds greatly attenuated them, other cloud types and combinations could even increase them through scattering effects.
In general, according to the Cancer Aid, clouds only reduce UV radiation intensity by 10 to 50 percent. They do not offer reliable protection, especially during lunchtime.
The same applies to tanned skin: Apart from the fact that the skin reacts to stress, it only corresponds to a sun protection factor of around 4. Every sunscreen has more.
German Press Agency (dpa)
Downs, C. et al. (2021): Benzophenone Accumulates over Time from the Degradation of Octocrylene in Commercial Sunscreen Products, retrieved on 05/09/2022: https://pubs.acs.org/doi/10.1021/acs.chemrestox.0c00461