Lipid (Lipid) is a general term for neutral fats, lipids and their derivatives, whose common physical properties are insoluble in water and soluble in organic solvents (e.g., ethanol, ether, etc.). There are two main types of body fat: 1, storage fat, such as neutral fat, mainly distributed in the subcutaneous, kidney, pancreas and other parts; 2, structural fat, such as lipids (phospholipids, glycolipids, cholesterol, etc.), mainly distributed in the cell. Neutral fat (Neutral fat) is a lipid composed of three molecules of fatty acids and one molecule of glycerol, which is neutral. Neutral fat is one of the ways of storing energy, which is released during oxidation. Neutral fat staining is often used Sudan Ⅱ, Sudan Ⅲ, Sudan Ⅳ, Sudan black B, oil red O method, etc. Neutral fat in tissues is hydrolyzed and free from fatty acids in certain disease processes, and fatty acids are detected in tissue sections, which is helpful to understand certain lesions, and it can be observed by using Nair Blue Sulfate staining.

Nair blue staining solution (Cain method), also known as sulfate Nair blue staining solution, can identify neutral fat and acidic fat (fatty acids or phospholipids, etc.) within the tissue, such as for atherosclerotic foci, acute hemorrhagic pancreatitis fat necrosis, the staining solution can distinguish between the two types of lipids, the appearance of acidic fat within the adipose tissue, that is, that is to say, there is neutral fat decomposition.