[Mostly relevant for people from developing countries]
I wrote this content  for an information campaign  I did at the university through nature-club. 
Most people spend as much as 80%-90% of their time indoors. The indoor environment of homes and offices is often more seriously polluted than outdoor atmosphere. The major sources of indoor air pollution are gases and particles that are released into air. Inadequate ventilation makes the situation much worse! 
 
Indoor Combustion

Combustion of fuels such as oil , gas or kerosine inside a building contributes to the concentration of VOC*s, particulate matter, oxides of nitrogen, oxides of sulphur, carbon monoxide, hydrocarbons and other odur causing chemicals. They can cause nose and throat irritation, headaches, asthma and even cancer!

Environmental Tobacco Smoke

Do you have someone in your family who smokes tobacco ? Tobacco smoke contains a complex mixture of over 4000 compounds, more than 40 of which are known to cause cancer! Many of the reaminign compunds are strong irritants. Tobacco smoking is responsible for approximately 3000 lung cancer deaths every year in non-smoking adults and causes respiratory infections in thousands of children .

 
Latex Paint

Latex paint contain VOCs* such as toluene, ethyl benzene, 2-propanol and butane. Some interior latex paint can emit formaldehyde when it is dying. These formaldehydes combine with other contaminants to cause headache, respiratory irritations, watery eyes, nausea , akin irritaion and heart problems. 
 
How to Avoid indoor air pollution
 

• Ensure effective ventilation in all the areas of the house.

• Install and use exhaust fans in kitchen and bathrooms

• Dont smoke at home or permit others to do so

• Choose quality building and furniturishing materials, which are free from formaldehyde

• Keep children awat from high risk areas, because they are the most vulnerable to health effects.