Storage conditions of the skin affect tissue structure and in vitro percutaneous penetration

For logistic and practical reasons it is difficult to perform in vitro studies on percutaneous penetration on fresh human skin obtained directly from surgery. Skin samples are therefore often kept frozen until use. The present chapter present the available literature on the topic. Storage of human skin at -20oC causes structural changes in the upper Stratum Corneum observable with image techniques such as multiphoton excitation fluorescence microscopy. The presently available literature does, however, not support that the observed structural damage to the integrity is sufficient to cause a general and significantly increased in vitro percutaneous penetration across human skin stored at -20oC. Use of skin stored at -20oC for in vitro studies on percutaneous penetration therefore seems acceptable as long as the barrier integrity is documented. Storage of human skin at -80oC causes significant structural changes in upper as well as deeper parts of Stratum Corneum. These more severe changes corresponds to significantly increased percutaneous penetration of chemicals applied to skin specimens stored at very low temperatures. Storage of human skin for later use in in vitro studies on percutaneous penetration is therefore not recommended at these low temperatures.