Cute as they may be, rubber duckies (and other toys like them) provide ideal conditions for bacterial and fungal growth — and the sudsy moist environment of a bath favors that growth too.

Dark side of bath toys. Credit: Andri Bryner, Eawag.

Oh no, science is taking our rubber ducks!

The study was carried out by a group of Swiss and US researchers. Over a period of 11 weeks, they carried out experiments with real toys, exposing them to either clean or dirty bath water, which contains things that you’d expect to see there (such as soap and bodily fluids). They found that “diverse microbial growth is promoted not only by the plastic materials but by bath users themselves.”

“Dense growths of bacteria and fungi are found on the inner surface of these flexible toys, and a murky liquid will often be released when they are squeezed by a child,” the Swiss government statement said.

But the real kicker came when they cut the rubber duckies into halves: researchers found between five million and 75 million cells per square centimeter were observed on the inner surfaces, and some of the bacteria species were quite worrying. Researchers also point out that bathing only in clean water reduces the chances of bacteria and fungal infestation.

“Fungal species were detected in almost 60 percent of the real bath toys and in all the dirty-water control toys,” the statement said.

“Potentially pathogenic bacteria were identified in 80 percent of all the toys studied, including Legionella and Pseudomonas aeruginosa,” which is often the culprit in hospital-acquired infections, it added.

Relax, no one’s taking your ducks away

This isn’t really unexpected — any plastic material you dunk into bathwater is bound to promote the growth of bacteria and fungus. But having a clear, quantified description of what happens on and inside of the plastic is, of course, an important step in directing evidence-based policy. However, researchers say, you shouldn’t throw away your rubber duckies just yet — in fact, the bacteria they hold might actually be helping children’s immune systems.

“This could strengthen the immune system, which would be positive, but it can also result in eye, ear, or even gastrointestinal infections,” microbiologist Frederik Hammes pointed out in a statement.

Instead, researchers call for tighter regulations on the polymeric materials used to produce bath toys.

Journal Reference: Lisa Neu et al. Ugly ducklings—the dark side of plastic materials in contact with potable water, npj Biofilms and Microbiomes (2018). DOI: 10.1038/s41522-018-0050-9