Leather is made from animal skin through complex physical and chemical processes. During the tanning process, various acids and alkalis are added to treat the leather, various fatliquoring agents are added for fatliquoring, various fillers are used for filling, and finally, finishing agents are used for finishing. Due to the smell inherent in the raw leather and various leather chemical materials used in the tanning process, the unique smell of leather is formed. Due to different types of raw hides and different leather chemicals used, the smell of leather can vary from light to heavy. For example, leather added with fish oil will more or less have a fishy smell; Leather coated with solvent based finishing agents may have some odor of solvents, etc; In leather and fur products, there is also the smell of adhesive, and even the smell of formaldehyde and benzene. Obviously, some toxic and harmful gases are harmful to human health. In the standard "Determination of Leather Odor" (QB/T2725-2005), the odor level is divided into five levels:

Level 1: No noticeable odor;

Level 2: Slightly odorous but not noticeable;

Level 3: Obvious odor, but not unpleasant;

Level 4: Strong, unpleasant odor;

Level 5: Very strong unpleasant odor.

Leather and its products, due to their unique characteristics, more or less have some odors, but in automotive cushion leather, sofa leather, and other leather, the odor of leather should be controlled.