Substances that cause irreversible damage and destruction of the skin are classified as “corrosive.” In the process of permanently damaging the skin, corrosive substances also cause it to swell and become discolored, eventually forming bloody scabs as it dies. Information about a substance’s ability to cause skin corrosion is required by the U.S. Department of Transportation (DOT) before companies can ship it from place to place. Corrosion is also an endpoint in skin tests mandated by the U.S. Environmental Protection Agency in its assessment of pesticides.
Rabbits’ backs are shaved and a test substance is applied to the shaved skin. The site is covered with a gauze patch for up to four hours, after which the patch is removed and the remaining substance wiped away. A wound is allowed to develop at the site for up to 14 days, and the degree of skin damage is then assessed. A chemical is considered to be corrosive if, by the end of the 14-day observation period, the wound is marked by ulcers, bleeding, bloody scabs, scars, and other visible signs of dead tissue. There is no requirement that animals be provided with pain-relieving drugs during this prolonged process.
Fortunately, three validated tests for assessing skin corrosion are available to replace the use of rabbits in painful experiments. The first of these methods, Corrositex™, was approved for use by the DOT in 1994 and ultimately published by the Organisation for Economic Cooperation and Development (OECD) in 2006 as OECD test guideline (TG) 435. Using a protein membrane instead of skin, Corrositex™ can measure whether, and at what rate, a chemical is capable of penetrating the simulated skin barrier according to a color-change reaction. Following the approval of Corrositex™, developers pioneered the reconstructed human epidermis (RHE) test method (OECD TG 431), which uses cultured human skin cells instead of live rabbits, and the transcutaneous electrical resistance (TER) test method (OECD TG 430).
Use of these replacement methods has dramatically reduced the number of rabbits used in skin corrosion testing across most agencies, but there is more work to be done before all agencies in all countries recognize that non-animal methods can provide all the information needed to ensure that chemicals are transported safely.
Stay tuned for more information as we make further progress with international regulatory agencies.