Most air purifiers work in one of three ways, and some utilize all three modes of cleaning the air:  High-efficiency particulate air (HEPA) filter: These are pleated mechanical filters that work by forcing air through a very fine mesh to remove pet dander, dust, pollen, mold, bacteria, and other airborne particles. HEPA filters are the gold standard. Activated carbon filters: These work to remove odor from the air by absorbing it. UV filters: These use lights to inactivate germs and bacteria. They’re often used in conjunction with HEPA filters.