It can be a number of things, but the most common problem is worn valve guides.
Burning oil
Could be a diesel? If not then replace your oxygen sensor on your exhaust. A bad oxygen sensor causes the exhaust smoke to be dark in color.
if it is white smoke engine need to rebuilt.
White smoke means head gasket, cracked head or equivelant.
Piston rings or Rich oil .
Head gasket
Black smoke means you're burning fuel, blue smoke, you're burning oil, white smoke, you're burning coolant.
grey exhaust smoke is caused by your engine burning oil during the combustion process. this could be caused by a piston ring that doesnt properly seal, or another leak in your engine.
bad head gaskets, or a crack in the block or head.
If you mean the smoke it's usually related to the quality of petrol
Black smoke coming out of the exhaust of a car is usually due to oil being burned in the engine's cylinders. This can be caused by a worn piston ring or rings.
what is the worst for your health breathing in tobacco smoke or exhaust fumes