Well the whole point is that they have been causing lots of harm all that time - lung diseases have always been one of the major killers. According to the New South Wales Health Department, tiny particles in the air kill about 400 people each year prematurely, in that state. In the USA, it's thought that dirty air, mainly from burning stuff, kills tens of thousands of people each year. Many of us have had the experience of being unable to open a window, because of the smoke from our neighbour's fire. But the effect of wood smoke goes beyond having your hair and clothes smell of your neighbours' smoke.
Wood smoke can cause irritations of the nose, throat and sinuses.
It can trigger coughs, asthma, bronchitis, emphysema, pneumonia, middle ear infections, cardiovascular disease, and even lung cancer. The smoke from a wood fire has tiny particles floating in the air. There's a special jargon used to describe these tiny particles. Today, PM10s are defined as particles between 2.5 and 10 microns in size. The PM10 particles tend to fall to the ground fairly rapidly.