Technologies are generally described for monitoring dehydration levels of a subject using Radio Frequency (RF) dielectric resonant oscillators (DROs) that may be affixed to the skin of the subject. According to some example aspects, a sensor comprising a microstrip ring resonator may be affixed to the skin and used to determine the change in hydration of a person quantitatively and/or qualitatively. An RF emitter can be configured to emit a scanning signal to the sensor, where the scanning signal can be swept over a specified frequency range. The sensor is configured to resonate in response to the scanning signal, where characteristics of the sensors resonance (e.g., the specific frequency and &ldquoQ&rdquo factor of the resonance) is impacted by dielectric losses of the sensor to the skin due to hydration level of the subject.
