Now how

How do dragons breathe fire?


Dragons are one of the most prominent mythological creatures, appearing in pivotal roles in legends spanning the globe. In many cultures, dragons are depicted as symbols of power, but between Asia and Europe there is one fundamental difference: Asian dragons are typically benevolent creatures whereas European dragons are evil and known for laying waste to the land.

This is in part related to one of the main physiological differences between the two: the European dragon is fire-breathing. The Asian dragon is not. It’s much easier to ravage a town when all you need to do is blow to make all the fields and houses burn down to the ground.

The threat posed by a fire-breathing dragon’s mere presence makes them popular creatures not only in ancient Norse and Germanic mythology and historical literary works, such as Edmund Spenser’s The Faerie Queene, but in modern culture as well. J.R.R. Tolkien’s The Hobbit features Smaug as the main antagonist (pictured below), a fire-breathing dragon who laid waste to the town of Dale and drove the dwarves out of the Lonely Mountain, capturing all of its treasure.


Dragons are also featured in the Harry Potter series, in the fourth bok serving as the main obstacle in the first task of the Triwizard Tournament (the formidable Hungarian Horntail pictured below) and in the seventh book appearing as a guard at Gringotts Wizarding Bank.


In Game of Thrones, dragons were considered to be extinct for over a century and a half until Daenerys Targaryen (below with Drogon) reintroduced them to Westeros and Essos.


Judging from these examples, it almost seems as though fire-breathing dragons are a necessary element for a memorable fantasy universe!


The fire-breathing quality of dragons is possibly the most dangerous aspect about them. If we want to depict this aura of imminent danger more realistically in film and literature, though, then it’s important to provide a valid explanation for how dragons can perform this fearsome action.


In most stories, dragons are omnivores, meaning they have two different types of teeth: sharp teeth for tearing meat and flat teeth for grinding plants. Some writers have hypothesized that dragons might even use their flat teeth to grind rocks.

Grinding rocks doesn’t seem to be an action that would provide any nutritious value whatsoever, but it’s not unheard of in animals. For example, birds sometimes swallow rocks to aid in their digestion. Birds actually have two chambers in their stomach. The first chamber, the proventriculus, acts the same way human stomachs do, secreting acid for breaking down food.  But, since snacks like seeds and nuts are so hard, birds swallow grit and small rocks, which accumulate in the second chamber, called the gizzard. The gizzard grinds the swallowed rocks against the seeds, smashing the hard foods and aiding in digestion (“Bird Digestion”).

Dragons are known to feed on livestock (and occasionally humans…), so sometimes they might swallow such prey without bothering to completely tear the meat apart from the bones. The hard bones could prove to be an issue for digestion, giving dragons a need to grind up and swallow rocks to aid in the digestion process. However, unlike in birds, this process could actually also be responsible for providing dragons with their fire-breathing powers.

If we assume that dragons follow the same digestive process as birds, then dragons will have leftover food and acid remaining in its two stomachs after the digestive processes have been completed. Bacteria in the intestines feed on these undigested food particles and release intestinal gases composed of hydrogen and methane through the process of fermentation (Mayo Clinic staff).

In humans, these intestinal gases would be excreted through burping, bloating, and flatulence, but it can be speculated that dragons could actually store the hydrogen and methane in its body in storage sacs and call upon it for later use during fire production. I think a fire-breathing dragon is much more terrifying than a farting lizard.

Now for the flint – when a dragon grinds up large rocks, metal-rich rocks would leave residue on its teeth. Then, as the dragon releases its hydrogen- and methane-rich gas, the gas would mix with the oxygen in the air and be ignited against the metallic residue (Dove). As a result, this combination of rock-grinding and intestinal gas storage creates the perfect conditions for fire-breathing.

And there we have it! Fire is spewed from the dragon’s mouth.


It can only help the victims of dragon raids to understand the physiological processes by which they spout flames from their mouths. If the people of Berk in How to Train Your Dragon were better educated about this subject, perhaps they might have been able to protect their villages from being razed so often (before Hiccup stepped in and made friends with Toothless, that is).


Written by Constance Kaita

Works Referenced

Images courtesy of,,, and

“Bird Digestion.” n.d. Web. 9 July 2013.

Dove, Laurie L. “How Dragons Work.” 3 October 2011. Web. 9 July 2013.

Mayo Clinic staff. “Intestinal gas: The inside story.” 22 September 2005. Web. 9 July 2013.

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