There are two different kinds of houses viz., houses built in very cold region and houses built in, subtropical or tropical region.

In the first case doors and windows are closed always because of the cold climate. Here we have several possibilities of indoor pollution. These include the formaldehyde from wood and plywood, volatile organic compounds from paints and solvents, lead paint dust, air fresheners and scented products. Controlled fireplace can add a big portion to air pollution.

Pesticide sprays may be fatal in tightly closed house. Use of coal in chimneys produces carbon monoxide and there were accidental deaths. We should not forget that the dry cleaned cloths emit tetrachloroethylene for days after dry cleaning. Pet animals produce a lot of dust. Dust mites increase in number in cushion, mattress and sofa.

Air conditioning filters have often harmful bacteria. The pollen from the garden and atmosphere also contaminate the indoor air quality.

Fungus is also a problem in closed houses.

In the tightly closed houses we must open the windows completely for 10 minutes so that the whole air is exchanged. One window per room is enough and this is important for our health.

In our modern flat, the air is automatically sucked out regularly and the fresh air is supplied which is energy saving as well as healthy.

In tropical areas the air pollution from outside brings dust and poisons inside the house. We must keep not only the house but also outside clean so that there will be fewer diseases.