The summer is almost here, and that means it’s time to hit the beaches and lather up with sunscreen — but there’s something you should know beforehand.

The truth is that while sunscreen is usually effective in protecting sunburns, what you may not realize is that many sunscreens don’t do anything to protect against ultraviolate A light, which penetrates deeper into the skin and is a significant cause of skin cancer. And according to Consumer Reports, many of them don’t live up to the SPF claims on their labels.

The truth is that many people are too reliant on sunscreen to protect themselves from the harmful effects of the sun. Sometimes, it’s our fault: we don’t rub it on correctly or don’t use enough, or we forget to reapply after it’s largely washed off. But a lot of times sunscreens are advertising an SPF that doesn’t match up to Consumer Reports tests. The organization found that 43 percent of tested sunscreens failed to meet the sPF claim on the label.

Consumer Report has detected this pattern for the past four years, and each time half of them have come below the SPF number advertised.

“We crunched the data from four years of our sunscreen testing—104 products in all—to see how well sunscreens in general protect you against the sun’s UVB rays,” the statement reads. “Our findings were troubling, especially when it came to mineral products, often called “natural” sunscreens—those that contain only titanium dioxide, zinc oxide, or both as active ingredients. The Food and Drug Administration (FDA) doesn’t routinely test sunscreens; it requires the manufacturers to test their products. But in most cases the companies don’t have to submit their results, just keep them on hand in case the FDA asks to see them. What’s more, companies only have to test a sunscreen on people when a product rolls out or is reformulated.”