口干（英语：Dry mouth）或称口渴，是一种人类因体内水分不足而引起的感觉，发生时会感觉口中唾液不足，产生想喝水的感觉。

中医药学（一级学科）；诊断学（二级学科）；诊法（三级学科）

Xerostomia (also termed dry mouth as a symptom or dry mouth syndrome as a syndrome) is dryness in the mouth (xero- + stom- + -ia), which may be associated with a change in the composition of saliva, or reduced salivary flow (hyposalivation), or have no identifiable cause.