It is if both people are wearing it. https://www.cdc.gov/coronavirus/2019-ncov/more/masking-science-sars-cov2.html https://www.cdc.gov/coronavirus/2019-ncov/mo

It is if both people are wearing it. https://www.cdc.gov/coronavirus/2019-ncov/more/masking-science-sars-cov2.html https://www.cdc.gov/coronavirus/2019-ncov/more/masking-scien... It lowers transmission by 80%. Masks help more if the person who has it wears it since they won't be transmitting the virus.