As ever more coronavirus infections in the US are diagnosed, some companies have begun promoting air purifiers as an effective protection against the virus. However, scientists tell BuzzFeed News that air purifiers are not the best preventative measure against COVID-19.

One IndieGoGo air purifier campaign sent out an email titled “Fight Coronavirus with cutting edge tech,” saying that “This tech is being installed in hospitals in Wuhan.” It claims that the air purifier can “eradicate virus on a single air pass” in a fundraising video set to upbeat music. The company has raised nearly $7,000 via the campaign, and says it will ship the devices in April.

The issue, according to experts, are the air filters themselves. Most commercially available air purifiers are high-efficiency particulate air (HEPA) filters. They can remove many particles from the air, but coronavirus is too small to be affected.

“Your typical HEPA filter is not going to be able to remove coronavirus from the air,” said Dr. Erin Sorrell, an assistant professor of microbiology and a member of Georgetown’s Center for Global Health Science and Security. “The filter itself is .3 microns and the virus itself is roughly .1 microns.”

The IndieGoGo purifier, called Hextio, also advertises a UVC filter. Dr. Sorrell said a UV filter does kill some viruses, but won’t affect coronavirus as the HEPA filter is not fine enough to suck it up from the air. Even if it could, the process “typically takes about 15 minutes but it varies across viruses.” It’s not clear how long coronavirus would take to kill using UV, Dr. Sorrell clarified. Dr. Aaron Glatt, an IDSA spokesperson agreed, saying the exposure of the virus to UV light “would have to be significant, it could not just be for a second.”

Another air purifier, Molekule, is being tested for its ability to kill coronavirus, Bloomberg reports. Yet it is worth noting the company’s previous claims about the effectiveness of its $799 air purifier have been challenged and it subsequently agreed to withdraw many of them, according to a Wirecutter report.

“The best thing to do is to stay in a room alone if you’re sick,” said Dr. Glatt. “And an open window will probably clear out the room better than your typical air purifier.”

The best way to protect yourself from the virus is to thoroughly wash your hands, and to use hand sanitizer that’s above 60% alcohol content, ensuring you cover your entire hands and allowing the sanitizer to dry. It’s also key to physically distance yourself from anyone who appears to be sick in public and cover your mouth and nose if you yourself are sick.

“Portable filters are not going to be helpful in capturing coronavirus and could give someone a false sense of security,” Dr. Sorrell said.