Peptides are compound molecules that are covalently linked by various amino acids in a certain order through peptide bonds, and have certain biological activities. Their molecular weight is between that of amino acids and proteins. Generally, peptides contain two to nine amino acids. Depending on the number of amino acids in the peptide, there are various names for the peptide, such as dipeptide, tripeptide, tetrapeptide, pentapeptide, etc. Peptides composed of three or more amino acid molecules are called peptides, with a molecular weight below 10000 Da, and can pass through semi permeable membranes. In addition, some literature refers to peptides composed of 2-10 amino acids as oligopeptides (small molecule peptides); Peptides composed of 10 to 50 amino acids are called peptides; A peptide composed of 50 or more amino acids is called a protein, in other words, a protein is sometimes referred to as a polypeptide. Peptides, also known as peptides, were discovered in the 20th century.

Compared to protein substances, the spatial structure is simpler, more stable, and has lower immunogenicity. It can act on the skin system, musculoskeletal system, blood system, cardiovascular system, endocrine system, immune system, etc. With the rapid development of biotechnology, synthetic technology, and analytical technology, peptides have become an important field of life science research. Nowadays, peptide products have been widely used in many fields such as healthcare, health food, cosmetics, and new materials, especially in the pharmaceutical industry, where peptide drugs are playing an increasingly important role.