By Roni Caryn Rabin and Emily Anthes

Federal health officials on Friday updated public guidance about how the coronavirus spreads, emphasizing that transmission occurs by inhaling very fine respiratory droplets and aerosolized particles, as well as through contact with sprayed droplets or touching contaminated hands to one’s mouth, nose or eyes.

The Centers for Disease Control and Prevention now states explicitly — in large, bold lettering — that airborne virus can be inhaled even when one is more than six feet away from an infected individual. The new language, posted online, is a change from the agency’s previous position that most infections were acquired through "close contact, not airborne transmission."

As the pandemic unfolded last year, infectious disease experts warned for months that both the C.D.C. and the World Health Organization were overlooking research that strongly suggested the coronavirus traveled aloft in small, airborne particles. Several scientists on Friday welcomed the agency’s scrapping of the term "close contact," which they criticized as vague and said did not necessarily capture the nuances of aerosol transmission.

"C.D.C. has now caught up to the latest scientific evidence, and they’ve gotten rid of some old problematic terms and thinking about how transmission occurs," said Linsey Marr, an aerosol expert at Virginia Tech.

The new focus underscores the need for the federal Occupational Safety and Health Administration to issue standards for employers to address potential hazards in the workplace, some experts said.

"They hadn’t talked much about aerosols and were more focused on droplets," said David Michaels, an epidemiologist at George Washington School of Public Health and head of OSHA in the Obama administration.

He and other researchers expressed concern that the C.D.C. has not yet strengthened its recommendations on preventing exposure to aerosolized virus.

The new information has significant implications for indoor environments, and workplaces in particular, Dr. Michaels said. Virus-laden particles "maintain their airborne properties for hours, and they accumulate in a room that doesn’t have good ventilation."

"There’s more exposure closer up," Dr. Michaels said. "But when you’re further away, there’s still a risk, and also these particles stay in the air."

Donald Milton, an aerosol scientist at the University of Maryland, agreed that federal officials should provide better guidelines for keeping workplaces safe.

"We need better focus on good respirators for people who have to be close to other people for long periods of time," Dr. Milton said. "A surgical mask, even if it’s tucked in on the edges, is still not really going to give you enough protection if you’re in a meatpacking plant elbow to elbow all day long with other people."

Health care workers, bus drivers and other workers may also require respirators, Dr. Michaels said. Customers in retail stores should continue to maintain distance from one another and to wear masks, he added; good ventilation is paramount in these settings.

Dr. Marr pointed out that one updated page on the C.D.C. website, entitled "How Covid-19 Spreads," says that inhaling the virus when people are far apart is "uncommon." The statement is "misleading and potentially harmful," Dr. Marr said.

"If you’re in a poorly ventilated environment, virus is going to build up in the air, and everyone who’s in that room is going to be exposed."