Commercially available artificial human skin models developed in the early 1990s provided an extremely useful alternative for researchers studying in vitro skin corrosion and irritation, as well as topical responses and phototoxicity.  Prior to the development of models such as EpiSkin, EpiDerm, EST1000, and Living Skin Equivalent (LHE), in vivo tests on either human or animals subjects were a necessity.  The development of 3D epidermal models that accurately represented the functional responses of the various layers of the skin, reconstructed from human keratinocytes cultured on a collagen matrix, to in vitro treatments negated the need for invasive testing on subjects.