Peptides (sometimes also called polypeptides) are naturally occurring in the skin and are used, amongst other things, to encourage skin cells to produce more collagen, which is one of the major building elements of the skin; collagen being made of three polypeptide chains. If these are applied directly to the skin, this helps to tell the system that it needs to make more collagen. Basically, Peptides are part portions of proteins.
When applied directly onto the skin (that is, topically), lab-derived peptides can still boost our collagen levels. Peptide amino acid chains are small enough to penetrate the skin to trigger cell messaging and behaviour, including the production of collagen. Collagen molecules themselves are too big to enter the skin through a cream. In encouraging the development of collagen, elastin and keratin, peptides encourage a smoother and more resilient skin.
Whereas peptides are a helpful and proven ingredient for tackling the ravages of ageing, they are best used alongside other anti-ageing ingredients and should not necessarily be used alone. They are, though, very helpful for ageing or menopausal skin. Peptides can work seamlessly with retinol, hyaluronic acid, vitamins, SPF and essential fatty acids, without any kind of contraindication. They are also unlikely to cause sensitivity or redness.
Familiar variants which you may have seen include acetyl-tetrapeptides, tripeptide-1, matrixyl and Argireline and look for them in the ingredients tree of any products you may wish to buy. Note, though, that the word 'peptide' may be generally used to describe any short chain of amino acids, so that term may easily be used for marketing even if the product does not contain a known active ingredient.
Product ranges to look at, which make extensive use of peptides include NeoStrata, Medik8, Agera or HydroPeptide.