How does this dragon's self-defense mechanism not burn the user?

Question

A type of dragon in my world, simply named the Thick-horn, has a well-known mechanism to use to defend itself despite its clumsiness. They are freakishly large, tend to be slow, and find it hard to fly without leaping off of some sort of high place, despite their bird-like bones. Their kind tends to fight against each other and other species often, requiring them to use this ability.

They can set themselves on fire, everyone.

But even I'm not sure how this biological phenomenon works, and I want to get to the bottom of it. Simply, the dragons sparks fire in their own fur, which spreads but does not harm them. They are intelligent, but I don't see how they would get their hands on extremely rare and fancy materials due to their... animal status.

Less ramble, more dragons! How do these dragons set their bodies on fire like this, without harming themselves?

(Notes: Previously described: some sort of secretion through the skin, maybe take some inspiration from this.)

Answer 1

1: Cork skin. The bark of the cork oak is an adaptation to an ecosystem where fire is frequent. Cork is fire retardant and barely flammable, despite being made of tree stuff. Your dragon skin is similar - spongy and flame retardant. When the dragons catch fire their skin might blacken but does not burn, and its corklike nature insulates the meat below.

2. Flammable stuff. I propose two parts to this. The dragons have glands that secrete acetone or ethanol, both flammable and both produced by biochemical pathways. The other part is crude oil or tar. The dragons know where this stuff bubbles to the surface and they go roll in it when their gooey coat is getting low. Alternatively the dragons just have a lot of greasy sebum.

   The volatile acetone starts first and then catches the oily coat. It takes just a bit to get going.

3. Spontaneous oily ignition. Ignition is the trickiest part. Many schemes for this have been posited here on WB stack but here is a new one. Just as oily rags can catch fire if left in a pile to heat up, the dragons have greasy glands whose secretions are trapped in folds. These get very hot and stay hot, but the corky bark protects the dragons. On opening these fold and letting in the air, the greasy secretions burst into flame and that ignites the rest.

Answer 2

Monstrous Nightmare, anyone?

Do they have to have fur?

The Monstrous Nightmare exudes a flammable gel over its body, which it can ignite by a biologically-produced spark. Presumably, its scales are also flame resistant. Depending on how hot the fire actually burns, this isn't entirely implausible, especially if the gel's vapor is what is flammable, while the liquid gel actually acts as a thermal insulator. Alternatively or in addition, your dragon exudes something that puts the fire out when it starts to get too hot.

Basically, there are real substances you can apply to yourself and light on fire without actually hurting yourself (when used correctly, i.e. don't let the fire keep burning for too long). You should be able to take something like this and combine it with natural fire resistance to achieve your desired effect.