Talk:Estus Flask (Dark Souls II)/@comment-24949280-20140602162602/@comment-4511886-20140806101055

It's estus, we just don't know what estus is.

Could be fire. The Witch of Izalith had the Lord Soul of Life (the others being Death, Light and Dark), and manipulated fire. So perhaps fire is a symbol of, or has a connection to, life which causes the "fire of the undead" to have a healing effect, for undead of course. It is notable that the effect of resting at a bonfire is a flame covering the screen. This could perhaps represents the "rebirth" of life after fire has destroyed it. I've read somewhere that ash can be used as a fertilizer.

Could also be that it's a sort of concentrated "bonfire power" (note that this is not the same as the previously mentioned fire) where the Estus is some sort of liquid, "blessed" with the same power that makes bonfires heal undead when they rest at them.