Hyperoxia, also known as oxygen toxicity or poisoning, can happen when your body is exposed to pure O2 for too long. That's right - one of the gasses you need to survive can also poison you.
This is an issue for people who have lung disease and other ailments that prevent them from breathing properly without canisters of oxygen. Our bodies just can't handle pure oxygen for long stretches at a time, and one of the side effects is cell destruction inside the lungs. However, there could be a very simple way around this problem, if new research pans out.
They exposed rats to two oxygen mixtures, both with 98% O2, but one with 2% hydrogen, and the other with 2% nitrogen. The rats exposed to the nitrogen mix had trouble breathing and fluid in their lungs — in contrast, the hydrogen mix rats had much better breathing, and less swelling. They also had raised levels of hemeoxygenase-1, an anti-inflammatory protein that protects cells.
At this stage, the hydrogen therapy is only effective in rats, and we don't know how it'll play out for people who are on oxygen for days or months at a time. But if something as straightforward as spiking those oxygen canisters with hydrogen could improve it dramatically, this could be a significant breakthrough in patient care.