Use of guanine deaminase as a seborrheic keratosis diagnostic marker

The present invention relates to an age spot diagnosing composition comprising a formulation for measuring an expression level of guanine deaminase. More specifically, the guanine deaminase is provided as an age spot diagnostic marker so that possibilities of age spot generation and/or the age spot generation can be predicted and/or diagnosed in advance. Moreover, by using the diagnostic marker, an age spot which is a benign tumor and a melanoma which is a malignant tumor can be distinguished, so that appropriate treatment can be started early, and the expression and activity of the diagnostic marker can be controlled to be useful in development of age spot medicines.