Ozone is good in the stratosphere, roughly 10 to 30 miles above Earth’s surface, where it forms a protective layer that absorbs harmful ultraviolet radiation before it reaches the ground. At ground level, ozone is generally a pollutant that irritates lungs and damages crops. The simple rule: ozone up high protects life, while ozone down low harms it. But the full picture includes a few specific settings where controlled ozone use has real benefits.
The Stratosphere: Where Ozone Matters Most
The ozone layer sits in the stratosphere and acts as Earth’s sunscreen. It absorbs most of the sun’s UVB radiation (wavelengths between 280 and 320 nanometers), the type most responsible for sunburn, skin cancer, and cataracts. It completely blocks the even more dangerous UVC radiation, which would be lethal to most life on Earth’s surface without that shield.
The ozone layer thinned dramatically in the late 20th century due to chemicals like chlorofluorocarbons (CFCs) used in refrigerants and aerosols. International action through the 1987 Montreal Protocol phased out those chemicals, and the layer is now recovering. According to a 2022 assessment from the World Meteorological Organization, the ozone layer is expected to return to its 1980 levels by around 2040 for most of the world, by 2045 over the Arctic, and by 2066 over the Antarctic, where the damage was most severe.
Water Treatment and Sanitation
Ozone is one of the strongest disinfectants available for treating drinking water. Many municipal water systems use it to kill bacteria, viruses, and parasites without leaving the chemical taste that chlorine does. It breaks down quickly into ordinary oxygen, so it doesn’t linger in the water the way other disinfectants can. Cities across Europe and North America have used ozone-based water treatment for decades.
In food processing, the picture is more nuanced. Ozone dissolved in water has been studied as a way to sanitize fresh produce, but research from the University of Arkansas found that washing vegetables in ozonated water at 5 parts per million for 60 seconds was no more effective than washing them in plain water. Ozone does work well in other food applications, like sanitizing equipment surfaces and processing lines, where it can be applied at higher concentrations in controlled settings.
Dentistry and Wound Care
Ozone gas has gained traction in dentistry as a disinfectant for deep cavities. Delivered through a specialized handpiece, it kills bacteria, viruses, and fungi in decayed tooth tissue. A systematic review in the International Journal of Clinical Pediatric Dentistry found that ozone therapy reduced bacterial counts in deep cavities, with one study showing a 68% reduction in total bacteria after ozone treatment. Another found significant reductions in cavity-causing bacteria that persisted at 6 and 12 months after treatment.
That said, ozone doesn’t always outperform conventional disinfectants. In some of the same studies, chlorhexidine (a standard dental antiseptic) achieved higher overall bacterial reduction, reaching 90% in one trial compared to 53% for ozone. The advantage of ozone is that it’s chemical-free and breaks down into oxygen, making it a useful complement rather than a replacement for traditional methods.
Industrial Applications
Beyond health care, ozone is used in laundry facilities, swimming pools, and wastewater treatment plants. Hotels and hospitals use ozone-based laundry systems because ozone disinfects fabrics in cold water, saving energy. Aquariums and fish farms use it to keep water pathogen-free without adding chemicals that could harm aquatic life. In each of these cases, ozone works well because it can be generated on-site, used in a controlled environment, and allowed to dissipate before people are exposed.
Worker safety is a real concern in these settings. OSHA sets the permissible exposure limit for ozone at just 0.1 parts per million over an 8-hour workday. Even small amounts inhaled over time can cause chest pain, coughing, and throat irritation, so industrial ozone systems are designed to contain the gas and ventilate work areas.
Where Ozone Is Not Good
Ground-level ozone, the main ingredient in smog, forms when pollutants from cars, power plants, and factories react with sunlight. It triggers asthma attacks, reduces lung function, and damages crops. This is the ozone you hear about in air quality alerts during hot summer days.
Ozone generators sold as home air purifiers are another case where ozone does more harm than good. The EPA has been clear on this point: at concentrations safe enough for people to breathe, ozone has little ability to remove indoor air contaminants. To actually break down pollutants like mold, smoke, or volatile chemicals, the ozone concentration would need to far exceed safe levels. Worse, ozone reacting with household chemicals can create new irritating byproducts, meaning the air quality may actually decline.
The pattern is consistent. Ozone is beneficial when it sits miles above you in the stratosphere or when it’s used in controlled, enclosed systems where humans aren’t breathing it in. In open air at ground level, whether from pollution or a plug-in device, it’s a respiratory hazard with no upside.