Abstract: The present invention relates to sensor for indicating a cumulative time period of presence of an ambient relative humidity, there the sensor comprising an indicator and a carrier and the indicator being located at one or more limited portions of the carrier. The carrier allowing migrating of the indicator within the carrier and the indicator causing an extension thereof by migrating from the one or more limited portions when the ambient relative humidity level exceeds a predetermined level. Further, the extension by migrating being detectable by a user and the cumulative time period being related to the extension by migrating and the characteristics of the indicator and the carrier. The present invention also relates to a method for reading the cumulative time period of presence of an ambient relative humidity indicated by a sensor and a method for providing a sensor for indicating a cumulative time period of presence of an ambient relative humidity by providing a carrier with an indicator.