The fact is that we need clean air for good health. The main reason why fossil fuels are bad for our health is because burning them releases a number of extremely harmful gases, such as carbon dioxide and monoxide, sulfur oxides, nitrogen oxides, and hydrocarbons.his is the gas that is emitted the most when fossil fuels are burned. In fact, the amount of carbon dioxide released into the atmosphere is now over 25 percent more than it was 150 years ago. Fossil fuels are also responsible for the increase in nitrous oxide and methane levels in the atmosphere.