Around the nation, drugstores have sold out of surgical masks. Schools have closed, sports games have been called off, and doctors’ offices — and their phone lines — are jammed. The truly anxious confess that they are trying to avoid touching elevator buttons, library books and the knobs on bathroom sinks.

As the number of confirmed swine flu cases in this country continued to rise to over 100 on Thursday, precautions over the illness — many of which appeared to be overreactions — were beginning to affect the daily lives of tens of thousands of people, even in states where the flu has yet to be found.

In interviews from Boston to San Francisco, some people said they faced a troubling, often internal balancing act over an illness no one seems to know much about: How, given alarming expressions like “imminent pandemic,” to keep their families safe (Should we cancel that playdate?) without succumbing to measures that might only breed more fear (What would people think if we actually wore face masks?).

In Cold Spring, Minn., on the same day a probable case of the flu was identified there, Diane McDonald and her two children had grown ill. Ms. McDonald, like thousands of others around the country, was panic-stricken, and called her doctor, who reassured her that her family’s symptoms did not match those of swine flu.

“You’re always out trying to protect your babies,” Ms. McDonald, 34, said, “and when you’ve got these scary things like this stupid pandemic of swine flu, you kind of want to duct-tape your windows and shut your house off to the world.”

In some places, doctors said they had been overwhelmed with patients, some of whom insistently sought tests for swine flu though they showed nothing of the fever and cough consistent with it.

“They’re coming without any symptoms; they just want to be checked,” said Ana Marengo, a spokeswoman for the Health and Hospitals Corporation, which operates the public hospitals of New York City. “It’s definitely crowding all our emergency rooms.”

In New York, where 49 cases have been confirmed and 16 more were suspected, some hospitals have reported healthy people — the “worried well,” in the words of some health officials — returning from vacation in Mexico and going straight from the airport to the emergency room. The city’s public hospitals reported 100 to 135 more patients each day in each emergency room since the outbreak.

In a nation suddenly doused, it seemed, in antiseptic hand gel, the worry was widespread. More than 300 schools closed around the country, sending more than 170,000 students home in 11 states, including all schools in the Fort Worth district.

In Delaware, a rap concert was canceled. At Slippery Rock University of Pennsylvania, 22 students who had been student teaching in Mexico were told not to take part in graduation ceremonies. (Their separate ceremony will be shown on videotape, school officials said, during the official event.) And in Chicago, some Roman Catholic priests stopped giving communion wine and were asking parishioners to avoid shaking hands. “The handshake of peace will be the nod of peace for now,” the Rev. Joseph M. Jackson of St. Ignatius Church said.

By no means was everyone concerned. In some places, in fact, people seemed perplexed — even mocking — at the thought that anyone would change their behavior given the relatively small number of confirmed cases in the United States and an illness that has, so far, caused only one fatality in this country.

On Thursday, people milled around parks, museums and malls as ever. In downtown Chicago, Jacqueline Reise was still trying to decide whether to go forward with a long-planned trip to Mexico on Saturday. “I’m not really worried,” she said. “I’m just not.”

The vast range of responses to the outbreak was precisely what had left some people, they said, torn about whether to be worried. Some complained bitterly about the news media’s “over-hyping” of the matter.

Others said they were confused by what they described as mixed messages from government leaders, including Vice President Joseph R. Biden Jr., who caused a stir in a television interview on Thursday when he seemed to say that neither he nor his family would travel in “confined spaces” like airplanes or subways. (His office quickly issued a clarification that Mr. Biden was urging sick people to stay out of such spaces.)

Still others said they felt fine until they started receiving e-mail messages from their companies, their children’s schools, their neighborhood groups — alerting them, in most cases, simply that the flu situation was being monitored.

For some, the worries over the flu (which despite the efforts of public health officials, no one seems to be calling 2009 H1N1) had created a new set of social politics.

A child’s cough in a downtown Chicago lobby drew stares on Thursday, then a scolding from a red-faced baby sitter: Cover your mouth. Parents said they were suddenly more judgmental about whose children seemed to be going to school sick and whose were not going to school at all.