Do air purifiers help with cat allergies?

Modestly, yes. True-HEPA air purifiers remove dander particles from the air, and the studies that have looked at allergen levels in homes find measurable reductions with consistent use. Two practical notes. One: “HEPA-type” or “HEPA-style” filters aren’t true HEPA and aren’t worth buying for this purpose. Look for the True HEPA label or H13/H14 ratings. Two: a unit sized for the room matters more than a small one running in a large space. For most apartments, a single right-sized purifier in the bedroom (where the allergic person spends 6-8 hours overnight) gives more relief than a smaller one in the living room. They’re a useful piece of the dander-reduction stack, not a standalone fix.