The Food and Drug Administration granted emergency authorization Tuesday to Ellume's over-the-counter antigen COVID-19 test for fully at-home use.

Why it matters: Once available, a person in theory would be able to buy the test in a drug store, swab their nose, and run the test for results in about 20 minutes.

• The company anticipates selling the test at about $30 or less. Ellume's goal is to produce 3 million tests by January and to deliver 20 million tests by the first of half of next year.

The big picture: Currently, home kits that test for the novel coronavirus either still need a prescription or require swabs be shipped to a lab, which could take days for results.

How it works: The rapid test can be used by symptomatic and asymptomatic users ages 2 years and above. This type of test detects fragments of proteins of the SARS-CoV-2 virus from a nasal swab sample.

• A clinical study demonstrated overall sensitivity of 95% and specificity of 97%, according to Ellume.

Yes, but: Like all other antigen tests, "a small percentage of positive and negative results from this test may be false," the FDA notes.

• "Patients without symptoms, positive results should be treated as presumptively positive until confirmed by another test as soon as possible."