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.

　　碱烧伤的致伤机制是碱有吸水作用，使局部细胞脱水，碱离子与组织蛋白形成碱-变性蛋白复合物，皂化脂肪组织，皂化时产生的热可使深部组织继续损伤。由于碱-变性蛋白复合物是可溶性的，能使碱离子进一步穿透深部组织，引起损害。

　　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.

　　苛性碱烧伤深度通常都在深二度以上，刺痛剧烈。溶解性坏死使创面继续加深，焦痂软，呈黏滑“肥皂样”或“烂豆腐”状变化，感染后易并发创面脓毒症。指甲接触苛性碱后会变薄、失去光泽，使指甲扁平以匙甲。稀薄溶液的接触可使皮肤干燥、皲裂、蜕皮。苛性碱的蒸汽对眼和上呼吸道刺激强烈，可引起眼和上呼吸道烧伤。

　　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.