Lactoferrin is a bioactive glycoprotein found in the whey protein fraction of bovine (cow) milk. Lactoferrin is considered a multifunctional protein, playing several biological roles, having antibacterial, antiviral, antifungal, anti-inflammatory, antioxidant and immunomodulatory qualities.The possible antibacterial activity of supplemental lactoferrin might be accounted for, in part, by its ability to strongly bind iron and Iron is essential to support the growth of pathogenic bacteria. Lactoferrin may also inhibit the attachment of bacteria to the intestinal wall. A breakdown product of lactoferrin is the peptide lactoferricin. Lactoferricin, classified as a bioactive peptide, may also have antibacterial, as well as antiviral, activity. The possible antiviral activity of supplemental lactoferrin may be due to its inhibition of virus-cell fusion and viral entry into cells.

Similarly Lactoferrin's possible antioxidant activity can also be accounted for by its ability to strongly bind iron. Free iron is a major contributor to the generation of reactive oxygen species via the Fenton reaction.

Lactoferrin's possible anti-inflammatory action may be accounted for by its possible antioxidant and immunomodulatory activities.