A frequent air exchange indoors it is more necessary than useful. To have a feeling of comfort and sufficient energy, each person needs at least 25 cubic meters / hour of vital air (technically: individual air cube).
It is not a problem of bad smells, but of health. In fact, below the threshold we have said, symptoms begin to appear that without air exchange they can gradually worsen: headache, visual disturbances, weakness, breathlessness, deconcentration. All effects of a malaise from lack of air affecting the central nervous system.
For just change the air open windows. It is true that the air inside the buildings comes naturally from the outside and that if you live in the city, perhaps on the ground floor overlooking the street, the air is generally not the best. However, air a little polluted by traffic and smog is better than stagnant indoor air.
L'air of the inhabited rooms must be continually renewed, especially if they are places frequented by many people such as classrooms and offices. THE air changes they must be the more frequent the smaller the rooms are and the more they have good windows.
The lack of drafts (which depends on the quality of the windows) is positive for thermal insulation but does not help air exchange, which is not helped even by the windows placed on one side: windows open on two sides allow for fast and effective ventilation. If there are no windows, or if they cannot be opened, they become indispensable devices for purify the air.
In the closed environments personal hygiene is even more important, but it should not be understood only with washing properly. The abuse of deodorants and perfumes can be equally annoying and harmful in the absence of adequate ones air changes.
In addition to ensuring a frequent air exchange, the good rule of hygiene for a healthy coexistence in confined spaces provides: absolute abstention from tobacco smoke, abundant use of water for daily hygiene, washing the hair every two days (every day would be damage to the hair), fresh clothes and natural fabrics (synthetics 'react' worse to perspiration), adequate nutrition for the season (helps the body to bear better).
To realize that the air is stale, however, you shouldn't wait until you feel bad. A little common sense is enough and, if you want to be picky, you can also measure the air quality moment by moment, using the right tools. For example, the lamp that measures clean air in the house.
And if you are interested in an air ionizer, a device that I recommend for the home because I was able to test it (and the price seems good to me) isAirfree AE60