A head gasket is the most important mechanical seal in your entire engine. Sealing the engine block and the cylinder head, the head gasket seals in the internal combustion process and also ensures that no oil or coolant leak into your cylinders. Without the head gasket, the engine would ultimately fail although not right away.
Blown head gaskets are usually caused by your engine overheating. A blown head gasket will not contain the combustion gases inside the cylinder creating a loss in power. However, the real damage comes from engine coolant leaking into the cylinders which may require new heads or a new engine all together.
The symptoms of a blown head gasket are white smoke from the tailpipe, bubbles in the radiator, white or milky oil, water leaking from the tailpipe, and engine overheating.
Make sure to keep an eye on your engine's temperature gauge. If the engine is running hot, make sure to get it checked immediately.