Use of at least one complex form of calmodulin-like skin protein (CLSP) (A) derived at least partly from a polypeptide of amino acid sequence encoded by a nucleic acid sequence of SEQ ID NO: 1 (comprising a fully defined 858 base pairs as given in the specification) or its analog or fragment, as in vitro or ex vivo characterization tool of a chronological aging of an epithelium, is claimed. Independent claims are included for: (1) process-I for non-invasive characterizing an epithelium condition, comprising: (a) determining a content of at least one complex form in a sample of the epithelium surface； and (b) comparing the content determined in step (a) at a reference value； (2) process-II for screening of anti-aging active ingredients, comprising: (a1) contacting, at least one cell type containing the complex form with at least one anti-aging active ingredient to be tested, under conditions favorable to the expression of the complex form； (b1) determining a content of the complex form； and (c1) comparing the content determined in step (b1) at a content of the complex form determined in the absence of chemical or biological compound to be tested； (3) cosmetic process to characterize the effectiveness of a cosmetic or therapeutic treatment to prevent and/or treat the signs of skin aging linked to chronological aging in an individual, comprising at least qualitative and quantitative characterization of the complex form； and (4) non-therapeutic process, for characterizing the effectiveness of a treatment capable of preventing and/or treating the signs of skin aging in an individual, comprising: (i) placing at least a first sample of skin surface representative of the person； (ii) quantifying the level of the sample particularly using enzyme-linked-immunosorbent assay technique, at least as complex form； (iii) repeating the steps (i) and (ii) on a second sample of skin surface representative of the individual； and (iv) comparing the results obtained from steps (ii) and (
