Sodium hydroxide and potassium hydroxide are the most harmful alkaloids to skin in alkaline substances, which are called caustic alkaloids. Caustic alkali has strong irritation and corrosiveness.
The mechanism of alkali burns is that alkali can absorb water, dehydrate local cells, form alkali-denatured protein complex between alkali ions and tissue proteins, saponify adipose tissue, and heat generated during saponification can continue to damage deep tissue. Because the alkali-denatured protein complex is soluble, it can further penetrate into deep tissues and cause damage.
Caustic alkali burns are usually more than two degrees deep and have severe stabbing pain. Soluble necrosis makes the wound continue to deepen, eschar is soft, showing a slippery "soap-like" or "rotten tofu" shape changes, after infection, vulnerable to wound sepsis. Nails become thinner and less lustrous when exposed to caustic alkali, making them flat and even spoonnails. The contact of dilute solution can make the skin dry, chapped and molted. Caustic alkali vapor strongly stimulates the eyes and upper respiratory tract and can cause eye and upper respiratory tract burns.