Late on Friday the Centers for Disease Prevention and Control (CDC) updated its guide on COVID masks and respirators, emphasizing the fact that N95s and KN95s are more effective against the spread of the virus when worn correctly. This comes during a weeks-long surge of cases in the US, due to the highly contagious Omicron variant.

The agency’s website now reads: “While all masks and respirators provide some level of protection, properly fitted respirators provide the highest level of protection. Wearing a highly protective mask or respirator may be most important for certain higher risk situations, or by some people at increased risk for severe disease.”

The page also notes: “Some masks and respirators offer higher levels of protection than others, and some may be harder to tolerate or wear consistently than others. It is most important to wear a well-fitted mask or respirator correctly that is comfortable for you and that provides good protection.”

N95 and KN95 masks—also known as respirators—were quickly identified as the safest face coverings early in the pandemic, followed by surgical and cloth masks. For the first many months, health officials asked members of the public to use non-valved cloth masks and save other PPE for frontline workers and severely ill individuals. But now due to increased production and availability, the CDC has removed mention of a supply shortage from its website.

N95, KN95, and surgical masks are made of multi-layered propylene plastic, which is better than cotton and other woven fabrics at filtering out the small aerosolized particles that carry the coronavirus through the air. N95 and KN95 designs have to meet high health standards both in the US and overseas. There are other types of industry-grade, but less-common respirators that provide protection against the virus; the CDC has a full list on its website.

[Related: The ultimate guide to reusing and buying N95 masks]

The changes had been anticipated by several experts earlier in the week. At a press conference on Wednesday, CDC Director Rochelle Walensky addressed the question of whether the US government would be able to make N95 and other high-quality masks more available in light of the recent Omicron surge. The CDC “continues to recommend that any mask is better than no mask. And we do encourage all Americans to wear a well-fitting mask to protect themselves and prevent the spread of COVID-19, and that recommendation is not going to change,” she said. Walensky added that the updated information on the CDC’s website would serve as a guide to “the different levels of protection different masks provide. And we want to provide Americans the best and most updated information to choose what mask is going to be right for them.”

For those wondering how to interpret the recent changes, if you’re living, working, or traveling in settings with a high risk of COVID exposure, you might want to upgrade to a respirator. Just note that they are disposable, so the longer you rewear one, the less effective it’ll be. As the CDC mentions multiple times on its website, a snug, comfortable fit is also important—perhaps more so than the type of mask. Be vigilant of fake N95 masks too: This detailed diagram can help you tell a real model from a counterfeit.

Labeled N95 mask diagram

Given that most respirators are sized for adults, they may not be suitable for kids, especially those under the age of 3. The CDC also lists an FDA-approved clear-panel mask for individuals with disabilities and those living or working with them regularly.