Filters need regular cleaning depending on air quality and usage. Some have washable/reusable air filters that need to be replaced every 6-12 months depending on air purifier brand and air quality.
Clean air purifier air filters with a soft brush or wipes down occasionally to remove dust particles. As for air purifiers that are multi-stage, usually, the pre-filter needs cleaning at least once per month. The air filter needs cleaning once per week.