Should you trust "broad spectrum" label on sunscreens? (US)

In the US, since 2011, sunscreens need to pass a specific test to be allowed to carry a "Broad Spectrum" sun protection label. Sounds good - but can you trust this test?

The test is performed by the manufacturer and needs to be documented (in case you were wondering, FDA does not go out and test sunscreens for labelling purposes). The "Broad Spectrum" label test is a laboratory exercise, meaning that it is not performed with real humans in real life conditions. A certain amount of a product is applied to a standard plate with texture resembling skin, is exposed to an artificial source of the UVA radiation. The amount of radiation that passes through the plate with the sunscreen on is measured. Then, a point (a wavelength) at which 90% of the product's combined UVB and UVA absorption happens is determined, and it's called a "critical wavelength". If this point is at 370 nm or lower, the sunscreen passes the test and can carry the "Broad Spectrum" label.

What the test checks in practice is whether the sunscreen offer some protection in the UVA range. It doesn't help to determine how much UVA protection is actually offered. Two sunscreens can have an identical "critical wavelength", and have an identical "Broad Spectrum" labeling, but one of them would let through about 15% of the radiation in the UVA long range, while the other one will expose the skin to double that amount (30%).

The other issue with the "Broad Spectrum" label testing procedure is that it renders different results based on how the sunscreen is applied to the plate. If a specific film pattern is formed (which happens a lot in practice), a sunscreen can get a "pass" score without offering a proper UVA protection in real life.

The bottom line: unfortunately, a "Broad Spectrum" label on US sunscreens does not guarantee a good level of UVA protection. This is why I recommend, in addition to opting for sunscreens with the "Broad Spectrum" label, check the specific UV filters the product uses. These are listed under "Active Ingredients" on the US sunscreen label. If you do not see either of the filters known to be effective in the UVA range (that is Zinc Oxide, Avobenzone, or Mexoryl SX (Terephthalylidene Dicamphor Sulfonic Acid) among the active ingredients. chances are high that this product does not offer a proper level of UVA protection.