How a Hydroxyl Generator Works (vs. Ozone & Fogging)

If you have researched smoke odor removal, you have probably encountered terms like hydroxyl generator, ozone treatment, and thermal fogging. These are the professional tools that actually eliminate odor rather than mask it — but they work in very different ways, with important safety differences. Here is how each works and when each is used.

SECTION 01How a Hydroxyl Generator Works

A hydroxyl generator produces hydroxyl radicals — highly reactive molecules that occur naturally in the atmosphere (they are part of how the sun cleans the air). Inside the machine, UV light reacts with humidity and oxygen to create these radicals, which then break down odor-causing molecules, bacteria, and volatile organic compounds on contact. The key advantage: hydroxyl generators are safe to run in occupied spaces, so restoration can continue while the machine works.

SECTION 02How Ozone Treatment Works

Ozone generators produce ozone (O3), an unstable molecule that aggressively oxidizes and destroys odor molecules. Ozone is extremely effective and works fast — but it is not safe to breathe. Ozone treatment can only be done in unoccupied spaces, sealed off, with people, pets, and plants removed. After treatment, the space must be ventilated before it is safe to re-enter.

SECTION 03Hydroxyl vs. Ozone: The Comparison

SECTION 04Where Thermal Fogging Fits In

Thermal fogging is a third tool that works differently from both. It heats a deodorizing compound into a dense fog of tiny particles that penetrate the same cracks, pores, and cavities that smoke reached — following smoke's path to neutralize odor where it embedded. Because smoke penetrates deep into materials, thermal fogging is often essential for reaching odor that surface treatment and air-based treatment cannot.

Professional smoke restoration frequently uses these tools in combination: thermal fogging to reach embedded odor, hydroxyl or ozone to treat the air and surfaces, and source removal for the worst-affected materials. Read our full smoke odor field guide.