Certain masks may be worse than no mask at all, preliminary Duke study finds

A new study looks at which masks are best at limiting the spread of coronavirus - and which are worse than wearing no face covering at all.

ByABC7.com staff KABC logo
Tuesday, August 11, 2020
Best masks: Duke study shows which are most effective
Dr. Anthony Cardillo, CEO of Mend Urgent Care in Los Angeles, comments on a Duke study looking at the effectiveness of various face masks.

LOS ANGELES (KABC) -- As public health officials continually reinforce the message that face coverings can help stop the spread of coronavirus, many different types of masks have flooded the marketplace.

So which mask is best?

A new Duke University study examined a variety of masks to see which are most effective at blocking respiratory droplets to protect wearers and the people around them.


  • Surgical N95. This mask is manufactured to surgical standards to provide a tight seal around the face. However, because of a shortage, most experts ask members of the general public to avoid acquiring these masks so they can be reserved for health professionals.
  • Three-layer simple surgical mask. Widely available and found to provide the next-highest level of protection.
  • Cotton. The researchers examined several different types of cotton masks and found most of them were fairly effective, but described the best as a "Cotton-polypropylene-cotton mask."
  • By now we all know that N-95 masks are better than surgical masks which are better than cloth masks which are better than a scarf or bandana.


  • Fleece: The study found that this type of face covering is worse than no mask at all. The researchers found that fleece face coverings - for example, a gaiter neck fleece - actually break up respiratory droplets into smaller droplets rather than blocking them, releasing a larger number of individual droplets into the air. Those smaller droplets are lighter in weight and therefore stay airborne longer. "Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive," the researchers wrote.
  • Bandanas were also considered ineffective, though not quite as bad as no mask at all.
  • Knitted: These types of masks were not effective at blocking respiratory droplets.
  • Dr. Anthony Cardillo, a Los Angeles-based ER specialist who was not involved in the study, tells Eyewitness News his clinic has been advising patients to wear simple surgical masks while out in public. If those aren't available, cotton masks are a good alternative, he said.

    He added that people should avoid masks that have valves in them, even N95 masks, as those openings allow droplets to be exhaled.

    "So we want to counsel all people, everyone to be wearing a simple surgical mask when you're out and about. If you cant get your hands on one ... If you have to wear a mask, cotton mask three-ply is the third best."

    The full study can be found here.