Potentially harmful bacteria may likely be on board spacecraft and making that trip to outer space as well.

According to a new study published in the journal Microbiome, also probably blasting off into space are bacteria, viruses, and mold, as detected in dust particles collected from vacuum bags and air filter samples aboard the International Space Station (ISS).

Researchers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, led by JPL microbiologist Kasthuri Venkateswaran, identified the problem by sequencing genetic data from dust in a 40-month-old air filter and two used vacuum bags. The investigation involved experts from two NASA space centers, three universities, and a biotech firm.

The study did not conclude whether the bacteria were harming humans, but noted that these microorganisms could incite skin irritations or inflammation in space.

Contamination is a grave issue among astronauts, as dirt and dust there do not settle like they do on Earth but instead float in the air. Astronauts are also subjected to weaker immunity in the space environment, becoming more prone to infections.

The ISS is regularly maintained and follows cleaning protocols, including testing surfaces, air, and water, to keep the surroundings healthy. Astronauts are also provided first-aid kits and medical tools and equipment, and can consult with on-ground doctors or make an emergency retreat back to Earth in extreme situations.

Compounding the bacteria issue aboard spacecraft are factors such as microgravity, space radiation, constant human presence, and increased carbon dioxide levels.

A 2009 study found that Salmonella bacteria in space was up to seven times more dangerous there than on Earth. Through what is called “fluid shear,” it was tricked into behaving as it would do so in the human intestinal wall. Bacteria act “safe” and therefore more geared toward multiplying in space.

Separate studies discovered that bacterial strains such as Pseudomonas aeruginosa, E.coli, and staphylococci thrive better in space than on the ground.

Microbial ecologist Jack Gilbert said that further work is needed to analyze the findings, which did not discover pathogens and presented differences with the clean room that are “not remarkable.” The team will assess virulence by increasing the length of DNA chains to be sequenced as well as including viruses in the analysis.