O3 (Ozone) is effectively airborne bleach. The molecule is ‘happy’ to dump an oxygen and become O2, the last O needs something to bind to however. Large, complex hydrocarbons are particularly vulnerable to damage from this. Unfortunately, our bodies are basically made of complex hydrocarbon chains. While our skin is quite resistant to damage (we have an ablative layer of dead skin cells), our lungs and eyes aren’t. Ozone will do significant damage, in even small doses.

Luckily, the same thing that makes it dangerous also makes it unstable. O3 breaks down to O2 relatively quickly (20 minute half-life, I think). It’s also amazing at decontaminating and deodorising a room or building. Bacteria, viruses and VOCs(volatile organic molecules, aka smelly stuff) are particularly vulnerable to damage from O3. You just have to remove anything you don’t want to damage (like houseplants, pets, or children), and keep the place relatively sealed to not pollute the area too much.