In this work, we performed systematic studies on the oxidation of zinc nitride metastable layers using a climate chamber with controlled temperature and relative humidity. The electrical properties of the samples were in situ analyzed using a programmable microprocessor with a voltage divider, while the structural and optical properties were ex situ measured by scanning electron microscopy, elastic recoil detection analysis, and spectroscopic ellipsometry. Our results show that zinc nitride transformation proceeds in a top-down way, with a progressive substitution of N by O, which leads to the formation of pores and a remarkable swelling effect. The overall behavior is well explained by a universal logistic growth model. Considering this model, we successfully fabricated and tested a zinc nitride-based dehydration sensor for biomedical applications.