If you tend to kick off your shoes when you enter your home because you’re worried about harmful bacteria from the outside getting inside and making you sick, relax. But you might want to think twice about putting your feet up on your desk.

Charles Gerba, a professor and microbiologist at the University of Arizona, studied how many and which kinds of bacteria linger on the bottom of shoes.

In 2008, researchers tracked new shoes worn by 10 participants for two weeks and found that coliform bacteria like E. coli were extremely common on the outside of the shoes. E. coli is known to cause intestinal and urinary tract infections as well as meningitis, among other illnesses.

“Our study also indicated that bacteria can be tracked by shoes over a long distance into your home or personal space,” Gerba said in a statement.

Nonetheless, contaminated shoes are unlikely to make you sick, researchers said.

It’s possible to transmit germs from your footwear if you touch your shoes and then your face or mouth, for instance, or if you eat food that’s been dropped on the floor. But in the hierarchy of potential health hazards at home, bacteria-caked shoes rank comparatively low, according to Donald Schaffner, a food microbiologist at Rutgers University.

What is a hazard? That sponge sitting on kitchen sink, for starters. Sponges, which retain water and food particles, are a “cesspool” of bacteria, said Dr. Aaron Carroll, professor of pediatrics at the Indiana University School of Medicine in Indianapolis.

Outside the home, there are objects and surfaces that are frequently touched but seldom, if ever, washed, such as money, ATM buttons and gas station pump handles, he said, adding, “Focusing on people’s shoes feels like focusing on the wrong vector.”

Overall, experts emphasize that washing your hands with soap and water when you get home remains the most important health practice.

Lisa Cuchara, professor of biomedical sciences at Quinnipiac University, said that fecal bacteria were certainly transferred from your shoes to your floor at home but that “for most healthy adults, this level of contamination is more of a gross reaction than a health threat.”

Putting the threat in perspective, she noted that the floor in a public restroom has around 2 million bacteria per square inch. A toilet seat, on the other hand, has an average of about 50 million per square inch.

“Think about that the next time you place your purse or knapsack on the bathroom floor and then bring it home and put it on the kitchen table or counter,” she said.

If you are concerned about what two-legged residents track in, then what about your dogs?

“We don’t wash the dog’s paws every time he comes in the house, and I don’t want to think about where he’s been walking,” said Carroll.

Andrea Kaufmann of Cape May Court House, N.J., said she changed out of her shoes into slippers to keep dirt off the floors, but added that she has two Labrador retrievers.

“I could sweep and vacuum three times a day and still have dirt on the floors from the dogs,” she said. “They can’t take their shoes off.”

Considering the benefits of modern-day sanitation, vaccinations and health care, the likelihood of getting sick from our shoes is “infinitesimally small as to almost be unwarranted,” said Jack Gilbert, a professor in the department of pediatrics and Scripps Institution of Oceanography at the University of California, San Diego.

Gilbert, an author of the book “Dirt Is Good,” said there were theories suggesting that bringing elements of the outdoors indoors could help stimulate autoimmune systems, particularly in children.

So, back to the original question: When should you take off your shoes?

Beyond the obvious reason — to avoid tracking mud across a freshly cleaned floor — it can be helpful to take off your shoes if you have young children crawling on floors or people in the home who have allergies, because pollen can be transferred to floors, especially to carpets.

“In cases where your immune system is compromised — people who have cancer, have undergone an organ transplant, have an infection — then there is much more of a reason to take your shoes off when you come home,” Cuchara said.

There’s also an etiquette issue. If you are visiting someone who prefers that you take off your shoes, it’s good manners to abide by their wishes, said April Masini, who writes about relationships and etiquette for her website, Ask April.

“Even if you don’t see shoes at the entrance, you can always ask if your host would like you to take off your shoes upon entering,” she said.