It has been nearly five months since all New Yorkers were required by law to wear face masks in public spaces to combat the spread of coronavirus. Since that time, New York City has sought to distribute nearly 8 million face masks, both in the form of three-ply paper medical masks and cloth face coverings.

Early on, city officials issued simple advice for mask care: washing cloth masks and reusing paper masks as long as they did not get wet. But in a sign that mask wearing may be an aspect of daily life for an indefinite period of time, New York City officials on Thursday issued new guidance for proper mask care.

"Is it in good shape? Has it been soiled? Is it torn? Is there any reason it's time to replace it?" said Mayor Bill de Blasio during a press conference.

"Keep an eye on it," he added. "Think about how crucial it is to make sure that it's in good working order."

In a shift, the mayor suggested that paper or surgical masks should be discarded after five days, in addition to being immediately replaced if they become damaged, dirty or wet.

Cloth masks should be washed daily with soap and water, according to the city's health commissioner Dave Chokshi.

Chokshi, who joined the mayor at City Hall, urged New Yorkers to have more than one mask so they can alternate usage. He also recommended choosing a face mask or covering that fits snuggly against the sides of the face and completely covers the nose and mouth.

"Don't share them and store them somewhere where they won't be touched," he said.

He also said that parents should try to find masks specifically made for children, but masks should not be worn by those under the age of 2.

In general, mask wearers should be careful not to touch the front portion of the mask, but instead handle it only by the ear loops or ties.

Mask guidance has been evolving in the United States. The Centers for Disease Control and Prevention began recommending non-medical masks in April and has since stressed the wearing of masks or face coverings in preventing virus transmission.

The CDC does not currently recommend face shields or gaiters, noting on its website that "evaluation of these face covers is on-going but effectiveness is unknown at this time."

Last month, a Duke University study suggested that gaiters might be worse than not wearing any mask at all. The authors later tried to distance themselves from this finding, and a Virginia Tech professor conducted another study that disputed the idea that gaiters posed more of a risk.

The CDC has also warned that masks with exhalation valves should also be avoided.

The CDC suggests including your mask with your regular laundry, using regular detergent and the warmest water setting for the cloth. It also recommends putting the washed mask in the dryer at the highest heat setting until the material is completely dry.

Those who opt for washing their masks by hand should use a diluted bleach solution, the CDC says. The mask should be soaked in the bleach solution for 5 minutes.

Not everyone agrees with using bleach. Linsey Marr, a leading aerosol scientist at Virginia Tech who performed the study on gaiters, told the New York Times that chemicals like bleach or hydrogen peroxide will begin to degrade the fabric fibers of a cloth mask.

“Washing with soap and water should work,” Marr said. “I throw my cloth mask in the washing machine with the rest of the laundry and dry it on low heat."

In terms of frequency, the CDC states only that masks should be washed "regularly" as opposed to the city's daily recommendation.

Luke O’Neill, professor of biochemistry in the school of biochemistry and immunology at Trinity College Dublin, recently offered an easier rule of thumb for mask washing: “Treat it like your underwear."