Violet Affleck, daughter of the Hollywood stars Jennifer Garner and Ben Affleck, was photographed by paparazzi last month walking in Los Angeles with her mother. In the photos, she was wearing an N95 face mask, as she often is in public. Perhaps not remarkable in and of itself, but some online had questions.

“Why Does Violet Affleck Always Wear a Mask? Explained,” promised one recent headline. The article speculated that privacy, an indeterminate medical condition and “personal expression” were among the reasons for her choice.

On Tuesday, Ms. Affleck, 18, appeared to offer an answer. Speaking during the public comment portion of a meeting of the Los Angeles County Board of Supervisors, she revealed why she wears a mask while also demanding greater public access to masks.

“I contracted a post-viral condition in 2019,” she said. “I’m OK now, but I saw firsthand that medicine does not always have answers to the consequences of even minor viruses.”

Speaking briskly — her whole speech clocked in at just 59 seconds — Ms. Affleck warned about the risks of long Covid, a serious medical condition that can cause brain fog, chronic fatigue and other health issues, and is thought to affect millions of Americans. Ms. Affleck, a recent high school graduate who appears to be bound for Yale in the fall, called on officials to make masks available in government buildings, hospitals and jails.

“I demand mask availability, air filtration and far UV-C light in government facilities, including jails and detention centers, and mask mandates in county medical facilities,” she said. “We must expand the availability of high-quality free tests and treatment and most importantly, the county must oppose mask bans for any reason.”