髯口是京劇中的假鬍子，大致與人們日常生活中的成長歲月雷同。但在戲中的人物是否要掛髯口，要依據行當（腳色）來決定。掛了髯口的人物，除了代表年齡的正常成長之外，其中有因生理及基因上的變化，使得在鬚髮上各有特色。也會在特殊的因素下，由行當的改變而產生造型上不同的變化，更會在性格特色上，將人物設計在雙重造型皆可的行當上。因此，髯口在京劇中多用於淨、丑及老生的腳色，其中，會因特殊的因素，而做彈性的變化運用。這些變化運用也是京劇程式化中的突變特性，然而不清楚的人會不重視，不瞭解的會有疑問。因此，值得在此提出研究及說明。

"Rankou," is the fake moustache in Peking Opera, Though it seem that a character's "Rankou," was put on according to his age, the final decision was made on a proper appearance of a certain role type. "Rankou," will change depends on character's ages in plays, or other biological or genetically reasons. The change from one role type to another will coherently influence the design of hair and moustache, but in most cases, a character will be categorized into one role type than can make the two different costumes persuasive. In this sense, "Rankou," is usually to be seen with "Jing", "Chou", and "Laosheng". Sometime it will be used in some special circumstances. The different adaptations are part of the mutation in Chinese's opera's stylized performances.