CERAMIDE IN SKIN AND BLOOD 373 loss and foreign body invasion, and ceramides are the main effectors in the stage of barrier repair and participate in the proliferation and differentiation of keratinocytes together with sphingosine to maintain the functional metabolism of the skin. The process of cell proliferation and differentiation maintains the functional metabolism of the skin and participates in the immune response (14). It also plays an important role in apoptosis, growth, differentiation, aging, immune-related signal transduction, and apoptosis and also has cosmetic effects such as adhesion, moisturizing, and antiaging (15). In addition to the results obtained using high-performance chromatography, more than 300 other lipids were detected under positive ion conditions, mainly ceramide and TG. More than 30 species were detected under negative ion conditions, all of which were ce- ramides. In addition to the ceramide compounds of interest, other lipids have been iden- tifi ed, such as phosphatidylcholine, lysophosphatidylcholine, TG, sphingomyelin, phosphatidylethanolamine, lysophosphatidylethanolamine, etc. Methods of collecting Figure 4. After centrifuging, drying, dissolution, and recentrifuging, the fi rst-order extraction peaks of ceramide subclasses in the four blood samples were obtained by chromatography. Table II Major Ceramides Measured in Blood Samples Sample C20H39NO3 C42H85NO3 Area Concentration Average (ng/ml) Area Concentration Average (ng/ml) Sample 1 481,000 5.76 6.05 75,182,885 212.59 220.99 507,350 6.06 79,309,046 224.56 531,062 6.33 79,746,893 225.83 Sample 2 1,293,308 15.07 15.52 86,415,078 245.18 246.73 1,380,635 16.07 88,538,303 251.34 1,325,935 15.44 85,897,911 243.68 Sample 3 498,855 5.96 7.17 (5.38 × 200/150 = 7.17) 80,564,935 228.20 220.13 435,820 5.24 77,344,272 218.86 408,079 4.92 75,436,264 213.32 Sample 4 540,450 6.44 6.13 73,712,246 208.32 203.46 493,675 5.9 70,995,731 200.44 505,256 6.04 7,1,401,759 201.62

JOURNAL OF COSMETIC SCIENCE 374 skin SC include surgical resection, tape stripping, cyanoacrylate stripping, mechanical scraping, sanding, and organic solvent dissolution methods. Compared with other collec- tion methods, the cyanoacrylate stripping method selected in this study is simple, repro- ducible, and can extract lipids from the skin to the greatest extent in a noninvasive manner. In this study, HPLC was used with high-resolution MS and LipidSearch software to determine ceramide constituents in the skin and blood. The method is simple, rapid, has ultrahigh resolution, good stability, high sensitivity, and can be used for qualitative and relative quantitative analysis of ceramide in samples. Ceramide is les s in the epidermis and diffi cult to extract from the skin. Because of the complexity of various ingredients, it is diffi cult for the cosmetics industry to mass pro- duce them. A ceramide analog (pseudoceramide) was artifi cially synthesized (16). However, how to effectively produce pseudoceramides that are very similar to natural ceramides still needs further research. This study provides a methodological basis for the detection and extraction of ceramide content. The application of high-throughput liquid MS can thoroughly detect and explore the composition and proportion of each ceramide content and also explore the effect of different types of ceramide on the skin barrier. This research has great signifi cance for the future development of skin care products. According to th e number of C atoms, ceramides are divided into long-chain (C chain 40) and short-chain (C chain d 40) ceramides. Our research shows that long-chain ceramide is the main type in the skin, mainly C42H85NO3. The long-chain and short-chain ceramides were measured in the blood at the same time, and the long-chain ceramides were signifi - cantly higher in the blood than in the skin, which may be related to factors such as vascular endothelial cell metabolism or tissue density. There are different distributions of ceramide in different tissues of the human body. The long-chain ceramides present in the skin SC help maintain the skin barrier, reduce water loss, and participate in adhesion. The blood is rich in short-chain ceramides, induces apoptosis, and participates in processes such as differen- tiation and aging (17,18). It can be used as a new type of exogenous agonist to regulate tissue metabolism together with cytokines (19). Long-chain ceramide is part of intracellular signal transduction and induces cell migration (20), which may have synergistic effects with short-chain ceramides, which needs to be studied further. Of course, this e xperiment still had some limitations: the sample size is small, only the skin on the inside of the forearm is selected, the age range of volunteers is relatively small, and there may be some one-sidedness. In the future, ceramide contents of different indi- vidual ages and different body parts need to be further studied. It is also important to analyze differences in ceramide from different ethnic groups or any skin disease. The study used li quid chromatography mass spectrometer to effi ciently detect ceramides in the skin and blood and compared the types and contents of ceramide, which provided an effective method and basis for exploring the metabolic changes of ceramide in the skin barrier and various systemic diseases. ACKNOWLEDGMENTS This study was entirely funded by a grant from the Science &Technology Action Plans for the Prevention and Treatment of Major Diseases. We thank the Thermo Fisher Scientifi c (China) Limited for assisting with the experiment and data processing. We appreciate language editing assistance provided by DerMEDit (www.DerMEDit.com).