What is the best air purifier for removing allergens and irritants from the air? what to look for when buying one?

HepA filter: Air filters in studies, have modest effects in allergy treatment. A study combining Hepa filters with dust mite prevention, and pet avoidance showed better symptom improvement. Combining avoidance measures with intranasal corticosteroid medications likely is better, and treating underlying conditions that affect allergies can have better effects. Allergy shots are likely most beneficial.