Disclosed is an agent that suppresses a decrease in preservative ability in an amino-acid containing composition that has a sufficient preservative ability even if as low a concentration of preservative as possible is used in combination therewith. The agent that suppresses a decrease in preservative ability is of an amino-acid containing composition that contains D-amino acids. The aforementioned D-amino acids may be D-glutamic acid and/or D-lysine hydrochloride. The amount contained of the agent that suppresses a decrease in preservative ability in the amino-acid containing composition is 0.000015 mass% to 10 mas%, and may be used in combination with 0.01 mass% to 1.0 mass% of preservative. Provided is a cosmetic material that contains the aforementioned agent that suppresses a decrease in preservative ability in an amino-acid containing composition.本發明開發出一種即使與儘可能低濃度之防腐劑併用亦具有充分防腐力之含胺基酸組合物中之防腐力降低抑制劑。本發明提供一種含D-胺基酸之含胺基酸組合物中之防腐力降低抑制劑。本發明中,前述D-胺基酸有時為D-谷胺酸及/或D-賴胺酸鹽酸鹽。本發明之含胺基酸組合物中之防腐力降低抑制劑之調配量為0.000015質量%至10質量%,有時與0.01質量%至1.0質量%之防腐劑併用。本發明提供一種包含前述含胺基酸組合物中之防腐力降低抑制劑之化妝品。
