Based on the theory that "where

yin

accumulates， latent

yang

must exist"， the pathogenesis of burning mouth syndrome evolves from deficiency of healthy

qi

， to accumulation of

yin

， latent

yang

， and upward scorching of heat-toxin. The fundamental cause lies in the imbalance between

yin

and

yang

and the internal generation of

yin

pathogens. The retention and accumulation of turbid

yin

， which gradually transforms into fire， is considered the key pathogenic process， ultimately leading to the formation of latent fire that generates toxins and scorches the mouth and tongue， causing pain. Treatment follows the basic principles of "resolving accumulated

yin

， dispersing latent

yang

， and clearing heat-toxins"， with management tailored according to disease stages and syndrome characteristics. In the early stage， when

yin

stagnation needs to be resolved and latent fire mildly alleviated，

Mahuang Fuzi Xixin Decoction

（麻黄附子细辛汤） combined with

Gancao Xiexin Decoction

（甘草泻心汤） is used with modifications. In the middle stage，

yang

is activated while

yin

is regulated to clear and reduce latent fire，

Wumei Pill

（乌梅丸） combined with

Fengsui Elixir

（封髓丹） with modifications is employed. In the late stage，

yang

is warmed to attack

yin

and pathogens are eliminated to remove toxins，

Dahuang Fuzi Decoction

（大黄附子汤） combined with

Shengma Biejia Decoction

（升麻鳖甲汤） is used.