Sinapis alba L. (Sinapis Semen)
Nature and flavour. Pungent and warm; Lung and Stomach systems.
Traditionally classed as warming the Lung and transforming cold phlegm, moving qi and dissipating masses, and unblocking the channels to relieve pain. Recorded for cold-phlegm with congested breathing and cough, for fluid accumulation in the chest and in the joints, and for numbness and pain attributed to phlegm obstructing the channels. It is best known outside China as the mustard of the condiment jar, and the drug is the seed of that plant used medicinally. Topically it is the basis of the traditional mustard plaster, in which the point is deliberately to redden and even blister the skin. Its companion article 黄芥子 (Brassica juncea) is a different seed with a different pungency.
性味归经。辛，温；归肺、胃经。
传统归类为温肺化痰、利气散结、通络止痛。古籍用于寒痰壅肺之咳喘气逆、痰饮停聚胸胁及关节，以及痰滞经络所致麻木疼痛。它在国外最广为人知的身份是调味品芥末，入药者即该植物的种子。外用时是传统「白芥子灸」（发泡灸）的基础，其用意本就在于使皮肤发红乃至起泡。其并列的黄芥子（Brassica juncea）为不同种子，辛辣之性亦不同。
有明确伤害记载的是外用。以本品制成的芥末膏与「发泡」敷贴已造成化学性烧伤、全层皮肤损伤及持久瘢痕，其中也包括儿童，以及仅敷用了看似很短时间的人；灼伤程度随剂量与时间递增，主观感觉并不可靠。不可用于破损皮肤，不可用于儿童，不可加盖密闭以增强效力。其辛辣来自硫代葡萄糖苷水解生成的异硫氰酸酯，属接触性刺激物 —— 已有接触性皮炎报告。内服对胃肠道有刺激性，传统上有热证、阴虚及消化性溃疡病史者忌用。孕期与哺乳期安全性未确立。