Identification and Quantification of Short-Chain Aldehydes Generated from Hair by Ultraviolet Ray Irradiation

Abstract

Hair can be exposed to oxidative environments such as hydrogen peroxide in hair dyes and bleaching agents, ultraviolet (UV) ray irradiation from sunlight, catalytic conditions with heavy metal compositions, and oxidative air pollutants. Therefore, unsaturated fatty acids present in the hair could be oxidized to form lipid peroxides and finally converted to aldehydes as their end products. Lipid peroxides and aldehydes will cause hair damage at the molecular level by denaturing hair proteins, and furthermore most of the short-chain aldehydes are sources of malodor. In the present study, we identified and quantified volatile aldehydes generated from hair by UV irradiation. Fatty acids in the hair samples were analyzed by GC-MS and 13 kinds of them detected, the ratio of saturated to unsaturated being 1 : 2. The hair was irradiated with UV light (total amount 706.8 kJ／m 2 ) in a closed container, so that the generated gas was directly trapped in a solution of 1,3-cyclohexanedione (CHD) ． The resulting aldehyde-CHD derivatives were analyzed by LC-MS. Short-chain aldehydes, formaldehyde, acetaldehyde and propanal were detected, and the amounts of them generated from 100 g of hair were 3.3, 0.3 and 0.1 mg, respectively. These low molecular weight aldehydes may have been formed by the consecutive degradation (called Norrish type II reaction) of the long-chain aldehydes which are produced by oxidative cleavage of double bonds in the unsaturated fatty acids in the hair.