As a hair scientist, this author is hugely grateful that his test substrate is both readily available and biologically stable. Every paper or presentation by skin care colleagues who must procure and store porcine dermis and epidermis, or colleagues who carry out even more unpleasant practices for in vitro fingernail testing, serves as a reminder of this. Thankfully, hair grows at an average rate of around 0.5 inches per month and egresses onto the scalp in a biologically inert state. Therefore, samples can be harvested from willing donors and kept indefinitely without any special storage considerations. Acquiring 100–200 fibers from an individual can generally be performed without noticeable consequences, and such small samples can be utilized effectively in various single fiber testing protocols.