@merpreb My dentist's office says to buy them from a US company that tests them, and doesn't just accept the label. According to them, the ad should say something like "US tested." I just started looking for some - if I find what looks like a good source, I'll let you know.
Sue
PS Be wary of anyone selling "3M N-95 Medical Masks" - according to my sister who works there, even employees cannot buy them for personal use - the entire supply is committed to the medical industry - if you can find them you will pay a very high price per mask - in the area of $6-10 each (I used to pay $1.25 in quantity of 20.) You can still get a limited amount of the 3M industrial ones with exhaust port for yard work and similar - we see them at our paint stores, but again for a quite inflated price.

I heard you try to blow out a candle. It passes if you can't blow out candle with mask on. Then you pour water into the mask holding the straps. The mask should hold the water where none drips out. If the mask passes then I'm pretty sure it's real and not a fake. There has been a problem with people setting up shop and making masks with inferior materials. That's because masks have gotten so expensive and people are trying to make a quick buck. But I think anything you buy that's in stock in the United States is probably real. They would have to test before they ship to Americans because they would be liable if the masks are fakes. I worry most about people that are buying masks on-line and the masks are being shipped directly to customers from overseas.