microorganisms of human skin fl ora, triglycerides are partially hydrolyzed, producing FFAs, diglycerides, monoglycerides, and glycerol ( 10-12 ). In addition, continual removal of the uppermost layer of the skin leads to liberation, at the skin surface, of free and esterifi ed cholesterols along with FFAs. Several lipid classes are then present in SSLs, and the complexity of the mixture is emphasized by the structural microheterogeneity within each class.Hydrolipidic fi lm represents an important modulator of cutaneous barrier functions ( 1-5 ), particularly in SC hydration. Moreover, sebum transports antioxidants to the skin surface (e.g., vitamin E), preventing aging ( 3,13,14 ). Free fatty acids contribute to the pH of skin surface ( 15-17 ). A particular acid (sapienic acid, C16:1 ⌬ 6) exhibits strong innate antimicrobial activity ( 18 ). Sebaceous lipids are involved in some infl ammatory diseases such as acne ( 14,19 ), seborrhea, or dermatitis ( 13 ). Maintaining the stability of the amounts and composition of SSL is of major importance to preserving skin barrier properties. Moreover, information provided by SSL analyses, such as fi ne profi ling, squalene/cholesterol ratio, and intact glyceride patterns, contribute to the wide knowledge of physiological and pathological evolution of hydrolipidic fi lm.Our study falls within the framework of lipidomics, in which global SSLs profi les are determined in the entire sample, keeping the structural integrity of the compounds. Our purpose was to develop a simple analytical protocol using a noninvasive sampling method without timeconsuming sample preparation steps that would provide a qualitative characterization of individual SSL compounds and a quantitative evaluation of different lipid classes. SSLs are formed from a complex mixture of free fatty acids (FFAs) and neutral lipids arising from both sebaceous secretion and skin removal ( 6 ). Freshly liberated sebum contains predominantly triglycerides, wax esters, and squalene ( 7-9 ). Under the infl uence of lipase-producing Abbreviations: APCI, atmospheric pressure chemical ionization; CI, chemical ionization; EI, electron impact; FID, fl ame ionization detector; HTGC-MS, high-temperature gas chromatography-mass spectrometry; SC, stratum corneum; SSL: skin surface lipid; TIC, total ion current.