There are actually more reasons than it seems: outdated filters in the ventilation system, lack of regular cleaning, use of aggressive household chemicals, dry air in winter - all this creates a toxic environment. We breathe microparticles of dust, mold, harmful fumes that can cause headaches, air quality for asthma, allergic reactions. To change this, you should pay attention to professional cleaning of air ducts, use of air purifiers and regular ventilation.