Leather is made from animal hides through complex physical and chemical processing. During the tanning process, various acids and alkalis are added to treat the leather, various fatliquors are used for fatliquoring, various fillers are applied for filling, and finally, finishing agents are used for coating. Since the raw hides themselves have an odor, combined with various leather chemicals used in the tanning process, a unique odor of leather is formed. Due to the different types of raw hides and the different leather chemicals used, the odor of leather varies in intensity. For example, leather treated with fish oil will more or less have a fishy smell; leather finished with solvent-based finishing agents will have some solvent odor; in leather and fur products, there may also be the odor of adhesives, and even the odors of formaldehyde and benzene. Obviously, some toxic and harmful gases are detrimental to human health. In the standard QB/T2725—2005 "Determination of Leather Odor", the odor levels are classified into five grades:
Level 1: No noticeable odor;
Level 2: Slight odor, but not noticeable;
Level 3: Obvious odor, but not unpleasant;
Level 4: Strong and unpleasant odor;
Level 5: Very strong and unpleasant odor.
Due to their particularity, leather and its products will more or less have some odor, but the odor of leather should be controlled in cases such as automotive seat leather and sofa leather.
