Lye is extremely caustic. Contact with skin or mucous membranes causes burns and frequently deep ulcerations with scarring. Mists, vapors, and dust can cause small burns.
Eye contact causes severe damage, including blindness.
Lye-based liquids usually contain a warning to avoid squeezing the container, but carelessness could lead to a disfiguring splash on the skin or a blinding squirt in the eye. Products that contain lye in a pellet form sometimes require you to measure a spoonful out of an opening which is too small for a spoon to fit. This situation is very hazardous because lye-based pellets are easily spilled as one pours the product from the container onto the spoon. Be extremely careful when using lye-based products. Wear gloves and goggles in addition to protecting exposed skin.