The New York Times posted an article about possible indoor pollution causes and what you can do about it. What struck me was the inclusion of scented candles and incense as a major source of indoor pollution according to a study by the E.P.A. 

Cooking fumes (especially Teflon coated pans), cigarettes, fireplaces, and furnaces may cause a large percentage of other pollution. We no longer use Teflon coated pans because the fumes can injure pet birds (like little Julius, our late Pacific Parrotlet) and, after reading this article, have banned burning scented candles in the house.

Because this is something that I am rabid about because of my poor Julius, here’s the article. I make no claim to the writing, research, or artwork:
https://www.nytimes.com/2016/03/15/science/dark-wall-stains-may-signal-indoor-pollution.html?_r=0

Dark Wall Stains May Signal Indoor Pollution
By C. Claiborne Ray
March 14, 2016

Q. What could be causing black stains on the walls above each segment of our radiators? Could the heating fuel be leaking from the radiators into the air we breathe?

A. The stains are coming from the air, not the radiators, and while the furnace and the chimney should be checked, there are other possible sources besides heating fuel for the black material.

Such stains, called ghosting by building engineers, are caused by deposits of soot, dust or ordinary dirt carried by the air and then deposited on the walls or ceilings.

The pattern of the deposits depends on factors like air currents, gravity, electrostatic attraction and temperature and humidity differences. For example, the reason the stains mirror the radiator segments is probably that the wall temperature varies with the shape of the radiator.

One of the most common sources of soot is partly burned carbon fuel, but soot could come from cooking fumes, cigarettes and fireplaces as well as the furnace. A surprisingly big source of the carbon that causes ghosting stains is perfumed room candles, a 2001 review of previous studies found.

As for health risks, they are related to the size of the particles; the smaller the particles, the higher the risk, the Environmental Protection Agency says.

The visible soot can be a signal of the presence of the more dangerous microscopic particles, less than 10 micrometers in diameter, that can penetrate deep into the lungs and cause heart and respiratory illnesses. [email protected]