“I felt as if I didn’t matter,” said Ms. Santamaria, who earns $22 an hour.

While many Americans are fleeing their offices to avoid any contact with the coronavirus, low-wage janitors are sometimes being asked to do the opposite. Although millions of Californians have been ordered to shelter in place, janitors are still being asked to go into offices to battle the invisible germs that threaten public health, even as those germs, and the new, powerful cleaning solutions they are being asked to use, may endanger their own health.

They often operate without specialized protective gear. And the increasing demand for their services is adding new stress and risks.

Janitors cleaning the Amazon headquarters in Seattle complained that a new disinfectant they were asked to use made their eyes and skin burn. In San Francisco, janitors said they have been asked to clean offices without having been told that people who had or were exposed to the virus had worked there.

Janitors wonder why they are left in the dark when companies go to great lengths to ensure that the tech, finance and other workers occupying the buildings they clean are aware of the most remote possibility of coming into contact with the virus. It shows, they say, how disparities play out in a public health crisis — how their lives sometimes seem to be valued less than those of people with resources and power.

“None of our families should be treated as second-class citizens,” Olga Miranda, the president of the Service Employees International Union Local 87, told the janitors at 555 California last week. She had gathered the largely immigrant work force in a plaza in front of the building and told them to walk off the job to protest the cleaning company’s failure to notify them about the coronavirus case.