It is quite common to see news posts publishing about new risks associated with drinking coffee, or watching too much TV, etc. where it becomes hard for people to figure out with of these “findings” are truly credible or complete nonsense.
However, people have learned over time that certain things are unanimously known to be harmful. For example, it is well known that smoking can cause many illnesses including lung cancer.
The following are things that are often proven to be harmful to humans that may be of surprise to some people:
Most, not all, modern candles use paraffin wax (waste product that is chemically bleached); paraffin wax contains carcinogens such as benzene.
The very popular Yankee Candle that uses paraffin wax
An alternative to modern paraffin wax candles would be to use natural beeswax candles which were used traditionally before paraffin wax candles became popular.
The Truth About Scented Candles: https://www.haywardscore.com/articles/the-truth-about-scented-candles/
Many homes built before the 1980s were built using asbestos for flooring, ceiling, insulation, and other treatments. Over time, it became clear that asbestos caused dangerous lung conditions, including mesothelioma, asbestosis, and lung cancer.
Therefore, if looking for homes built before the 1980s, ensure that asbestos has not been used in, or has been safely removed from, the unit.
Some popcorn ceiling were formed using asbestos
Asbestos In The Home: https://www.cpsc.gov/safety-education/safety-guides/home/asbestos-home
Asbestos in the Home: https://www.mesothelioma.com/asbestos-exposure/jobsites/homes/