Why do commets have tails?

Comets have tails because when they approach the Sun, the heat causes their icy nuclei to sublimate, releasing gas and dust. This process creates a glowing coma around the nucleus and forms one or more tails that always point away from the Sun due to solar wind and radiation pressure. The tails can be made up of ionized gas (the ion tail) and dust particles (the dust tail), each forming under different conditions.