What is one reason why indoor air pollution has become an increasing problem?

Indoor air pollution refers to the burning of fuel sources to cook and heat the house for example. There are several reason why this type of pollution is an increasing problem, one of the most common is that indoor air pollution is from CO which is carbon monoxide, which is undetectable, it doesn't have any color or smell to know that we are breathing it.

In addition, indoor air pollution represents an important leading risk factor to death, around 1.5 million deaths per year. According to Our World in Data, in low-income countries, 6% of deaths is due to indoor air pollution.

Lastly, most domestic activities are based on burning fuels, that's why deaths rate are so alarming, because normal activities cause indoor air pollution.