Human serum albumin (HSA) is structurally stabilized by 17 disulfide bonds, and interactions between domains (or subdomains) of HSA also contribute to its stability. The effects of several other factors on the stability of HSA and pharmaceutical preparations that contain HSA have been widely investigated. When HSA is heated and in the presence of chemical denaturants, unfolding occurs through multiple steps, and the genetic variations of HSA and ligand binding to HSA have been shown to contribute to protecting HSA against such irreversible structural changes.