As the number of anthrax exposure cases grows across the country, so too do the hoaxes and the instances where harmless white powder has terrorized people.

Planes have made emergency landings and been quarantined. Stores, schools, government buildings and restaurants have been evacuated. Most of the culprits have been innocuous substances -- from flour and Old Bay seasoning to talcum powder and even confetti.

The fears were only compounded Monday when a letter sent to Sen. Majority Leader Tom Daschle’s office in Washington tested positive for anthrax.

It's a strange new world for Americans, and so far we don't seem to be coping very well.

"Because bioterrorism has never hit America before, people are afraid," said Health and Human Services Secretary Tommy Thompson on Fox News Sunday. "But there are a lot of false rumors out there."

Thompson and other health and science experts are trying to allay fears, pleading with the public to calm down.

"People should not panic," said Dr. R. John Collier, a microbiology professor at Harvard Medical School. Collier is working to develop an inhibitor blocking the anthrax toxin for a possible future cure. "They should simply be a bit cautious. Everyone is going to be fine."

He said the public should be reminded that only one person has died in the rash of recent anthrax cases and just a handful more have been exposed to the bacterium.

"It takes a lot of anthrax to make anybody sick and takes a lot more to kill somebody," said Michael Fumento, a senior fellow at the Hudson Institute who is writing a book about biotechnology. "But it only takes a single spore for a person to test positive. The threat of anthrax is grossly overstated."

So far, though, people don’t seem to be listening.

In Cleveland, Ohio, a plane was quarantined Monday afternoon when a white powder was spotted. Hazmat crews rushed to the scene, locking down the aircraft and keeping passengers onboard while they ran tests.

On Saturday in San Jose, Calif., a man who spilled confetti as he opened a greeting card onboard a United flight had a less-than-happy landing later.

Because some on the flight believed the tiny pieces of paper were anthrax particles floating through the air vents, FBI, police and hazmat teams were on the ground to meet the plane, and the man was stripped down, scrubbed clean and dressed in a rubber vapor-trapping suit.

Other flights were diverted or quarantined over the weekend and Monday because of errant baby powder and even, in one case, salt.

In Newtown, Conn., a woman seen sprinkling a white powder from her bag Saturday frightened people and brought officials to the scene. Authorities determined the substance was flour – often used by hikers like the woman in question to mark their trails.

The Sands Hotel & Casino in Atlantic City, N.J., closed for an hour Sunday after a prescription bottle containing white powder was found on a restaurant table. Authorities and rescue workers who responded found it was Old Bay seasoning left behind by a diner.

A South Carolina county library shut down for more than two hours Sunday when traces of an unidentified white powder – later determined to be benign -- were found on an audiocassette someone returned. The librarian had to be decontaminated.

In Monterey, Calif., firefighters barricaded an area around a pile of white powder in a hospital parking lot – which turned out to be baking soda. Chalk dust found outside a University of Virginia hall sparked a similar reaction.

Since the anthrax incident in Daschle’s office on Monday, politicians’ staff feel particularly vulnerable and jumpy. A D.C. employee of West Virginia Sen. Jay Rockefeller found powder on his pants as he opened a letter. Capitol police investigated and found the substance was from the latex gloves he was wearing when he handled the mail.

"Right now we resemble the world’s largest chicken farm with all of our heads decapitated at the same time," Fumento said. "If you were to paint a portrait of the American people right now, it wouldn’t be George Washington crossing the Delaware. It would be Edward Munch’s The Scream."

Fumento said the hysteria only inspires the terrorists and pranksters responsible for the scares. Speculation about all the possibilities doesn’t help, either.

"You’ve got to look at reality, not worst-case scenarios," he said. "We are making ourselves mentally sick. The more we panic, the more we tell them, ‘Do it again.’"

Instead, he advised, people should be a little more cautious – without overreacting.

"We need to be strong. We need to be brave," Fumento said. "What we need to do is what the terrorists dread the most: Go about and live our lives."

The Associated Press contributed to this report.