You may want to think twice about making that next cup of tea or coffee.

Up to 90 percent of mugs in office kitchens are coated in germs, research has shown, and 20 percent of those cups actually carry fecal matter.

According to University of Arizona professor of environmental microbiology Dr. Charles Gerba, who carried out the 1997 study, rarely changed communal kitchen sponges are the key culprit in spreading bacteria.

“Coliform bacteria were present on 20 percent of the coffee cups before and 100 percent of the coffee cups after wiping with a dishcloth or sponge,” Gerba writes. “No E. coli was found on cups prior to wiping. However, 20 percent of coffee cups were positive for E. coli after wiping.

“The presence of insanitary conditions in office kitchen and/or coffee preparation areas is of concern. The presence of potential pathogens in this environment necessitates the initiation of proper sanitary standards.”

If you want to avoid drinking your co-workers’ fecal bacteria, Gerba advises either taking your mug home each night and putting it through the dishwasher, or investing in a “small office cup washer.”

The study, “A Microbial Survey of Office Coffee Cups and Effectiveness of an Office Cup Washer for Reduction of Bacteria,” was first published in the journal Dairy, Food and Environmental Sanitation.

In 2012, a subsequent study led by Dr. Scott Kelley of the University of California found men’s offices had “significantly” more bacteria than women’s. The research team, which included Gerba, identified more than 500 bacterial strains, the most abundant of which came from human skin, nasal, oral and intestinal cavities.

The study found chairs and phones had a high abundance of bacteria, while the desktop, keyboard and mouse were somewhat cleaner. “Humans are spending an increasing amount of time indoors, yet we know little about the diversity of bacteria and viruses where we live, work and play,” Kelley said.

Researchers have also identified disgusting levels of bacteria on our smartphones. In 2011, a study by the London School of Hygiene and Tropical Medicine found one in six mobile phones in the UK was contaminated with fecal matter.

“This study provides more evidence that some people still don’t wash their hands properly, especially after going to the toilet,” said Dr. Val Curtis.

“I hope the thought of having E. coli on their hands and phones encourages them to take more care in the bathroom — washing your hands with soap is such a simple thing to do, but there is no doubt it saves lives.”

And it’s not just offices. From fast food chains and public pools to gym weights and dollar bills, it seems like anywhere researchers can think of running a swab, there’s poo to be found.

“We are bathed, as a society, in human feces,” NYU School of Medicine clinical professor of microbiology and pathology Dr. Philip Tierno told Marketwatch. “People spread whatever they have on their hands — like feces, which can be transmitted very easily.”

Tierno added that fecal matter could survive for days or weeks on surfaces, “so washing your hands is imperative — before you eat or drink anything, and before you touch your face.”

According to the Global Handwashing Day campaign, 3.5 million children under the age of 5 are killed every year by pneumonia and diarrheal diseases. Washing hands with soap is one of the most effective ways of preventing these illnesses.

In developed countries, handwashing helps prevent the spread of viral infections like norovirus, rotavirus and influenza.