Rules: Breath Weapons

A dragon’s breath weapon is a supernatural ability. It does not work in antimagic areas. Using a breath weapon is a standard action. As noted in the Monster Manual, when a dragon uses a breath weapon, it must wait 1d6 rounds before it can breathe again. In this case, a round lasts until the dragon’s next turn begins. For example, if a dragon breathes in the first round of combat, and the die roll for when the breath weapon can next be used is a 1, the dragon can breathe again in round 2. If the die roll is a 4, the dragon could not breathe again until round 5.
If a dragon has more than one type of breath weapon, it still can breathe only once every 1d6 rounds. The Recover Breath feat can shorten the time a dragon has to wait between uses of its breath weapon.
The size, shape, and effect of a breath weapon depends on the kind of dragon and its size and age, as given in the Monster Manual.