Ever looked at a sunscreen and wondered what the SPF rating really means? It turns out, you shouldn’t have had to worry about it, because a lot of them do effectively zilch.

That’s coming from a study out of Australia, which put several of the country’s top sunscreen brands to the test (brands which, it should be said, don’t sell exclusively in Australia).

Of the 20 brands researchers tested, they found that 16 didn’t meet the SPF listed on the packaging.

While a drop from SPF 50 to SPF 30 might not sound like the biggest deal, some of the drop-offs were much more severe. Despite strong regulation of the sunscreen industry in Australia, one of the tested sunscreens, “Ultra Violette’s Lean Screen SPF 50+ Mattifying Zinc Skinscreen,” had an SPF rating of just 4. Pretty far cry from SPF 50+!

Although that particular sunscreen has been pulled off the market, researchers are now calling for greater investigation into sunscreen sales worldwide, as many brands share formulas and manufacturers, and thus could be exposing their customers to the same issue.

So, in the last few days of summer, make sure you wear your sunscreen — and maybe switch up the brand a bit just for safety.