Until I started researching the ingredients in products, I always felt that lemon, orange or pine oils and smells were safe.
It turns out that this is not true! Oils derived from citrus implies safety, but sprayed into the air, they can react with trace levels of ozone air pollution to form ultra-fine particles that penetrate deep into the lungs and formaldehyde, which the U.S. government classifies as a known human carcinogen. The California Air Resources Board advises people to limit the use of citrus- or pine oil-based cleaners on smoggy days to avoid exposure to particulates and formaldehyde.