Science & ideas · The body & medicine

The gas you can't live without can blind you and cause seizures

Breathing oxygen at higher-than-normal pressure, something that happens to divers, patients in hyperbaric chambers, and premature infants on supplemental oxygen, can poison the body rather than sustain it. The damage shows up in three main places: the brain, the lungs, and the eyes. Short bursts of very high-pressure oxygen attack the central nervous system within minutes to hours, bringing on tunnel vision, ringing ears, twitching, and eventually a convulsive seizure that is especially dangerous underwater because a diver can lose their mouthpiece and drown. Longer exposure at lower, still-elevated pressures instead damages the lungs, starting as a tickle in the airway and progressing to coughing, chest pain, and eventually fluid buildup and collapsed air sacs, while prolonged high oxygen also harms the retina, causing short-sightedness in divers or, in premature babies, abnormal vessel growth that can detach the retina. At the root of all three effects is the same chemistry: excess oxygen generates reactive molecules that overwhelm the body's antioxidant defenses and start damaging cell membranes and DNA.

The practical history of the condition is really a history of protocols built to dodge it. Divers learned to calculate depth limits and an "oxygen clock" for how long they can safely breathe enriched gas mixtures, switching to helium-based blends when nitrogen alone would become dangerously narcotic at depth, and hyperbaric medicine staggers oxygen treatment with air breaks to avoid both seizures and lung injury. Newborn care went through a painful correction: doctors once poured oxygen into incubators, which caused an epidemic of infant blindness from retinal damage, and when oxygen was then cut back sharply, infant deaths from lack of oxygen rose instead, so modern units now carefully titrate and monitor blood oxygen to balance both risks. Research figures like Paul Bert and J. Lorrain Smith first identified the brain and lung forms of the condition in the late 1800s, and later work through the twentieth century, including extensive U.S. Navy testing, refined exposure limits and showed that most of this damage, even seizures and lung inflammation, tends to heal once oxygen levels return to normal. Screening tests meant to predict who is personally vulnerable have largely been abandoned because individual tolerance turns out to vary too unpredictably to be useful.

Outside clinical and diving settings, oxygen toxicity mostly surfaces as a public misunderstanding. Recreational "oxygen bars" and oxygen-massage gadgets have marketed extra oxygen as a stress reliever or hangover cure, claims regulators say aren't backed by evidence and that can actually be risky for people with heart or lung disease. Astronauts avoid the problem entirely by breathing near-pure oxygen at very low cabin pressure, since it's the pressure of oxygen rather than its percentage that causes harm. The idea of oxygen as a hazard even predates the science, turning up in a nineteenth-century Jules Verne story where a town is driven to aggression by a doctor's gas experiments, a tale the author himself admitted was pure invention rather than anything grounded in fact.

The two forms of oxygen poisoning were named after their 19th-century discoverers: the Paul Bert effect for the nervous-system version and the Lorrain Smith effect for the lung version.

Read the whole of Oxygen toxicity on Wikipedia

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