More than 100,000 varieties of face masks are currently for sale. They come in silk, cotton and synthetics; with filters and without; over-the-head and over-the-ears. They have sparkles and sunflowers; friendly greetings and insults; cartoon characters and teeny reindeer.

What they don’t have is a label that shows how well they block infectious particles, an omission that has frustrated public health officials during the coronavirus pandemic. Those experts note that there is a big range in the effectiveness of various designs, and some barely filter out particles at all.

“The most fundamental, basic question is: What is the safest mask and how do I assure that I have that, and my family members and children have that?” said Fran Phillips, who stepped down in August from her post as deputy health secretary of Maryland. “It’s so startling that we are here in this moment and we don’t have that information.”

That may change soon. A division of the Centers for Disease Control and Prevention is working to develop minimum filter efficiency standards, and labels showing which products meet them, for the vast and bewildering marketplace for masks and other face coverings.

The National Institute for Occupational Safety and Health, a division of the CDC known as NIOSH, has been quietly writing guidelines with an industry standard-setting organization, ASTM International (formerly the American Society for Testing and Materials), that are expected to be made public next month.

“By having a standard in place you will be able to know what level of protection is being achieved and you’ll have a consistent way of evaluating these products,” said Maryann D’Alessandro, director of the NIOSH National Personal Protective Technology Laboratory.

Since the pandemic began, there has been little federal oversight of masks and other face coverings. Both the Food and Drug Administration and the CDC have some authority over the industry. The FDA, which regulates medical devices, shares authority with NIOSH for oversight of N95 respirators, which are the most protective devices available. But most of the masks the general public wears are just pieces of cloth and don’t come under any regulatory oversight.

Sales of masks took off after the FDA issued an emergency measure in April that said in part that the agency would not take action against companies selling them to the general public. At the same time, however, the FDA also noted that these products “may or may not meet fluid barrier or filtration efficiency levels.” That warning didn’t hurt the market, and some critics now blame the FDA for the poor quality of many of the products being sold.

“There were many things the FDA could have done to improve the situation, especially after research started coming out about which masks worked and which didn’t,” said Diana Zuckerman, president of the National Center for Health Research, a nonprofit health policy group. “FDA could have issued a guidance that masks should be fitted, at least two layers of cloth, not made of stretchy materials, etc. Instead, there was a free-for-all.”

The effectiveness of masks can range “from 0-80%, depending on material composition, number of layers and layering bonding,” said Dale Pfriem, president of Protective Equipment Consulting Services and a member of the standards development working group addressing mask guidelines.

The gold standard for masks is the N95, which fits tightly and can filter out at least 95% of very small particles. But N95 masks are generally reserved for health practitioners, and they have been in short supply since the outbreak began. Hospitals, desperate for more N95s, have been driven to a booming black market to secure them.

To offset the shortage, the FDA last spring authorized the sale of the KN95, the Chinese equivalent of the American N95. But the agency soon detected fraudulent and counterfeit products and narrowed the field of permissible KN95 imports. Despite that, the agency acknowledges that there is still rampant fraud, with countless companies stamping ‘KN95” on masks that do not meet the FDA standards.

One step below the N95s in terms of protection are FDA-approved surgical masks, which must meet certain agency standards. The surgical mask style is often copied by companies that sell imitations which do not offer the same level of protection.

And then there is the Wild West: millions of masks fashioned from every possible fabric, from single layers on up, as well as bandannas and gaiters, which are closed loops of fabric that are worn around the neck and can extend to cover the lower part of the face.

Just about any mask is better than no mask, public health experts say. The CDC has updated its guidance on masks numerous times, noting that a tightly woven, multilayered fabric offers better protection for both the wearer and the people with whom the wearer comes in contact than a mask made from a single layer of fabric or a loose knit. But the agency’s website offers no clarity on whether masks with filters offer better protection than those without them, nor about how synthetic fabrics compare with cotton or other materials.

Jeffrey Stull, a member who is assisting in writing the standards, said the group would also rate masks and face coverings for “breathability.” The standard-setting project, he said, has been a long haul.

Manufacturers who want to note that they meet the ASTM standard must first have their products tested by an accredited laboratory. They should also be able to show that their masks provide a reasonable fit to the population at large. Those who do comply with the standards can then note that they meet the ASTM standard on the product or the packaging. There is no enforcement mechanism, however.

Daniel Carpenter, a professor of government at Harvard, called NIOSH’s work in developing the standard “regulatory entrepreneurship.”

“It’s saying, ‘Let’s use the tools we have, even if we don’t have formal regulatory tools,” Carpenter said. “It is an alternate mode of regulation. It can have a pretty important regulatory effect because if you don’t comply with the standards, you don’t get the seal of approval.”

Pfriem hopes the standards catch on. “What we have here is a really good standard,” he said. “Manufacturers will have something to design their products to, and something to put in their marketing materials and packaging, and consumers will have a sense of confidence.”

He added, “I can tell you that a lot of what is marketed on eBay and other sites, that are manufactured, say, in your neighbor’s garage, won’t be able to meet this standard.”