Dragon breath

Dragon breath, or breath weapon, known in Draconic as frahraek, was a term used to refer to a special ability that was inherent to dragons and the majority of dragonkind, even those who merely had draconic ancestry.

Nature of Breath
The “breath” aspect of "dragon breath" was a bit of a misnomer, as it was not discharged from the lungs through exhalation. Rather, its stream of energy was more accurately vomited.

Depending upon the type of dragonkind or draconic ancestry, a breath weapon had different properties. There were nearly as many varieties of dragon breath as there were types of dragons. Though a number of dragons possessed the same type of breath and some possessed two distinct breaths.

Biological
In true dragons, the elemental or magical energies that granted a dragon their breath weapon were said to be generated by the heart and suffused throughout their body within the blood. The source was previously thought to be a large blood vessel called the fundamentum, or draconis fundamentum, but that merely channelled energy from the heart to a chamber in the gizzard. This organ stored a dragon's magical energies until they were needed to be unleashed as dragon breath.

Some breath types required an instrinic temperature, which was maintained internally by the elemental or magical energy that flowed through a dragon's bloodstream. While other breath types, such as acid, didn't have any such necessities. Additionally, dragon eggs were inherently resistant to harm from the breath weapon of their parents, though this resistance waned the closer they came to hatching.

Magic
Dragon breath had an inherently magical nature to it. Some believed that the magic permeating the Prime Material plane empowered it. Others believed that the different species of chromatics, as well as metallics, were each imbued with elemental magic and their breath weapon was a manifestation of that elemental energy.

Sometimes, a dragon's breath could be affected by the magic that permeated within their lairs. Such as clinging to and lingering on those afflicted by it or recharging at an incredible rate.

Some individual dragons and creatures of draconic heritage were capable of channeling the destructive energy of their breath into some other magical or supernatural effect. For example, with sufficient practice some dragons were capable of shaping their breath weapon into a bipedal, elemental creature known as an animated breath.

There were a variety of spells that acted upon dragon breath. Such effects included compelling a dragon to exude their breath, diminishing a breath's effectiveness, suppressing a dragon breath entirely, or altering its appearance and properties. And some draconic spells&mdash;that being, spells unique to dragonkind&mdash;required the use of dragon breath to cast, such as dispelling breath.

History
On Toril, some scholars from Candlekeep proposed the proto-dragon theory, claiming that the dragons of their world gradually developed breath weapons through evolution. This theory purported that a common ancestor, ignidraco, developed a digestive tract that allowed them to regurgitate their own intestinal gas and ignite it with an enzymatic, hypergolic reaction in the back of their throats. The proto-dragon theory went on to claim that the ancestors of green dragons and black dragons developed their breath weapons from further modifying their digestive tracts.

There were many detractors to the proto-dragon theory, who pointed out that it could not fully explain the myraid of other elemental and non-elemental breath weapons that dragons possessed.

True Dragons

 * There were a number of chromatic and metallic species of dragons that had similar types of dragon breath.
 * Crossbreed dragons, those born through the mating of two different species, could potentially develop a breathe weapon that was a combination of both their parents'.
 * The three-headed species dzalmus had a breath weapon that was a life-draining gas, though only one of its heads could unleash it at a time.
 * Ethereal dragons had a breath weapon that was a cone of pure force, which uniquely could affect even creatures on the Ethereal plane.
 * Hellfire wyrms had a breath weapon that was a cone of hellfire, a magical fire that was unique to its homeplane of Baator.
 * Mist dragons possessed two breath weapons, one that was a caustic slime that induced nausea and another that was a scalding cone of mist.
 * The radiant dragons of Mount Celestia possessed two breath weapons, one that was a line of pure force that they reserved for earnest battles and another that was a blinding cone of radiant light, the latter of which they reserved for situations they wished to diffuse without causing harm.
 * The radiant dragons of wildspace had a breath weapon that was pure force, said to be similar to the spell magic missile but far more powerful. This could be exuded as one large, focused pulse or as six smaller pulses.
 * Rust dragons possessed two breath weapons, one that was acid and another that was an extremely corrosive liquid.
 * Salt dragons had a breath weapon that was a cone of sodium chlorine crystals.
 * Styx dragons possessed two breath weapons, one that was acid and another that was an intelligence draining gas.
 * Tarterian dragons possessed two breath weapons, one that was a line of pure force and another that was a cone of gas which sapped the will of its targets, an effect similar to the spell crushing despair.

Lesser Dragons

 * Dragon turtles had a breath weapon that was a cone of scalding steam.
 * The three-headed draken species could breath bolts of lightning. They could do this twice per day from each of their heads, but only from one of them at a time.
 * Dread linnorms, a two-headed species of linnorm, had a distinct breath weapon for each of its heads. One breathed fire, the other a freezing wind.
 * Faerie dragons had a gaseous breath weapon that induced feelings of euphoria.
 * Space drakes possessed a similar breath weapon to the radiant dragons of wildspace.
 * Stygian linnorms uniquely had a breath weapon that was a mixture of acid and water from the River Styx.

Dragonkind

 * Chimerae, dracimerae, and gorgimerae all could exude a breath weapon. In the case of a dracimera, this was dependent upon what chromatic ancestry it had. In the case of chimerae, which were not members of dragonkind, their breath was dependent upon what type of dragon their draconic head resembled. Most commonly, a chimera had a draconic head that resembled a red dragon and thus exuded a fire breath, while gorgimerae always had a red draconic head.
 * Most dragonborn were capable of exuding some type of dragon breath. The type of breath weapon was dependent upon what chromatic, metallic, or gem draconic ancestry the dragonborn had. And some believed that, like dragons, dragonborn were imbued with elemental magic. Some dragonborn whom believed this would claim that the dragon deity Io had gifted them that power as a sign of his favor. Regardless of its origin, it was typically as powerful as that of a wyrmling of the same type.
 * Most half-dragons were capable of exuding some type of dragon breath. Like dragonborn, the type of breath weapon was dependent upon the creature's draconic ancestry.
 * Weredragons could exude a limited dragon breath whose effects varied depending upon what type of dragon they resembled.

Magic

 * Rarely, weapons could be magically altered or enchanted to produce dragon breath.
 * The bulwark of the Great Dragon allowed its wielder to exude a fiery dragon breath three times per day.

Undead

 * Dragons resurrected as lesser forms of undead dragons lost their breath weapons, such as skeletons and zombies, though some sources claimed that zombies retained a weaker version of their breath weapon.
 * Dracolichs retained the breath they had in life, but were required to eat in order to refuel it.
 * The ghosts of dragons had their own unique form of breath that was a cone of gray mist, which sometimes took the form of a ghostly parody of the breath they had in life.
 * Hoarder dragons retained the type of breath they had while alive, but with an added spray of pelting coins