Yes, black soot from candles can be harmful. The fine particles of soot can potentially be inhaled into the lungs, causing respiratory issues, especially for those with pre-existing conditions such as asthma or allergies.
Extended exposure to black soot may also lead to other health problems. Furthermore, soot can be deposited on surfaces, which can damage the home's interior. Therefore, it is advisable to minimize the production of soot when using candles and to ensure good ventilation.