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.

　　堿燒傷的致傷機制是堿有吸水作用，使局部細胞脫水，堿離子與組織蛋白形成堿-變性蛋白復合物，皂化脂肪組織，皂化時產生的熱可使深部組織繼續損傷。由于堿-變性蛋白復合物是可溶性的，能使堿離子進一步穿透深部組織，引起損害。

　　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.

　　苛性堿燒傷深度通常都在深二度以上，刺痛劇烈。溶解性壞死使創面繼續加深，焦痂軟，呈黏滑“肥皂樣”或“爛豆腐”狀變化，感染后易并發創面膿毒癥。指甲接觸苛性堿后會變薄、失去光澤，使指甲扁平以匙甲。稀薄溶液的接觸可使皮膚干燥、皸裂、蛻皮。苛性堿的蒸汽對眼和上呼吸道刺激強烈，可引起眼和上呼吸道燒傷。

　　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.