The sensor is an electrical device and we have tested it in environments up to 90% RH so we cannot guarantee it will work being constantly over 90% RH as the device is not waterproof. However, the sensor electronic board has a special coating to prevent humidity corrosion, but we cannot guarantee it won't be damaged when slightly wet or over 90% RH. If you have a specific need to be over 90% RH, please email us at support@getniwa.com or visit our community forum.