Wearable sweat-sensing platforms represent a transformative advancement in noninvasive, real-time health monitoring, enabling personalized healthcare. For in vivo applications, sensor substrate materials require biocompatibility, secure adhesion, and, preferably, environmental sustainability. However, existing substrate materials fail to meet some of those requirements. This study introduces bacterial cellulose (BC) as a novel sensor substrate, leveraging its printability, biocompatibility, self-adhesion, and eco-friendliness. A wearable sweat sensor was fabricated by screen-printing conductive inks onto BC films. A key challenge addressed was the hydrophilicity of BC, which can cause liquid penetration and disrupt signal stability. To solve this, an approach was developed where the electrical tracks are sandwiched between two hydrophobic layers to fully avoid liquid interference and ensure stable electrochemical performance. The sensor was further functionalized with the alcohol oxidase enzyme to enable reliable alcohol detection in sweat at the relevant concentration range. This work demonstrates the feasibility of BC-based sensors for their application in wearable health monitoring, meanwhile promoting sustainable technological innovations in personalized healthcare and well-being technologies.