How Deodorant Fumes Contaminated the ISS Water Supply and Baffled NASA Chemists

In 2010, a year after NASA’s new water recycling system began turning astronaut urine back into drinking water, organic carbon levels aboard the ISS started climbing toward the safety threshold — a trajectory that would have forced NASA to either ship up fresh water or bring the crew home. Because the station has no onboard analytical chemistry capability, samples had to ride a Soyuz back to Houston, where lab chemists confirmed the contamination but couldn’t identify it. The culprit wasn’t among the hundreds of chemicals engineers had anticipated, nor in the lab’s mass spectrometry reference library. Boeing eventually pinned it down: dimethylsilanediol (DMSD), a breakdown product of siloxanes — the slippery silicone compounds in antiperspirant, wet wipes, lotion, and hair conditioner.

The identification effort itself became a casualty. NASA chemists destroyed three gas chromatographs before realizing the instruments’ own siloxane tubing was absorbing DMSD and contaminating every subsequent reading. Meanwhile, the mystery deepened when the station’s carbon levels spontaneously returned to normal. The eventual explanation: roughly 1.5 grams of siloxane vapor evaporates from crew hygiene products daily, gets broken down by space radiation into water-soluble DMSD, and collects in the water condenser. It binds only weakly to the filtration beds, silently accumulating until the resin saturates — then other compounds displace it all at once, producing dramatic spikes that subside once the backlog flushes out, and repeat with every filter replacement.

The episode illustrates a recurring engineering lesson: the most disruptive failure modes often come from mundane, ‘inert’ materials nobody thought to model. Siloxanes now shorten the life of the station’s 50-kilogram multifiltration beds, which must be replaced annually, and degrade the hydrophilic coating on a 70-kilogram heat exchanger that gets flown back to Earth each year for refurbishment. NASA can’t simply ignore the contamination, since DMSD spikes could mask more dangerous substances — so a chemical chosen precisely for being cheap, stable, and unreactive has become one of the most expensive recurring problems in the station’s life support loop.