伤寒头痛。何以明之。头痛谓邪气外在经络。上攻于头所致也。难经曰。三阳经受
风寒。伏留而不去。则名厥头痛。言三阳之经上于头尔。然伤寒头痛者。太阳专主
也。何者。以太阳之经起于目内 。上额交巅。上入络脑。经所谓太阳受病者。头项
痛。腰脊强。又曰七日病衰。头痛少愈。虽然。阳明少阳亦有头痛不若太阳之专主
也。盖太阳为病属表。而头痛专为主表证虽有风寒之不同。必待发散而后已太
阳病头痛发热身疼腰痛。骨节疼痛。恶风无汗而喘者。伤寒也。麻黄汤主之。太阳
病头痛发热。汗出恶风者。中风也。桂枝汤主之虽有伤寒六七日不大便。头痛有
热者。而与调胃承气汤下之者又云。若小便清者知热不在里。仍在表也。当与桂
枝汤以头痛未去虽不大便六七日。其小便清者。犹为在表。是知头痛属乎表者
明矣。头痛一切属三阳经也。而阴病亦有头痛乎。太阴少阴二经之脉。皆上至颈
胸中而还。不上循头。则多头痛之证。惟厥阴之脉。循喉咙之后。上入颃颡。连目
上出额。与督脉会于巅。病亦有头痛。经曰。干呕吐涎沫者。吴茱萸汤主之者是矣。
夫头者精明之府也。神明居之。小小邪气作为头痛者。必曰发散而可也。其或痛
甚。入连于脑。而手足寒者。又为真病。岂能发散而已哉。呜呼。头痛为外疾犹有不
可治者。又矧脏腑之疾乎。
伤寒病中的头痛，该如何阐明呢？所谓头痛，是指邪气在体表经络，向上攻冲头部所导致的。《难经》说：三阳经受风寒之邪，潜伏停留而不离去，就称为厥头痛。这是说三阳经的经脉上行至头部。然而，伤寒病中的头痛，主要由太阳经主管。为什么呢？因为太阳经起于目内眦，上行至额部，交会于头顶，深入络属脑部。医经上说，太阳经受病时，会出现头项痛、腰脊强直的症状。又说，病程到第七天病情衰退，头痛会稍微减轻。虽然如此，阳明经和少阳经也有头痛，但不像太阳经那样专门主管。大概太阳经发病属于表证，而头痛专门作为表证的标志，虽然有风寒的不同，但必须等待发散（解表）之后才能痊愈。
太阳病，出现头痛、发热、身体疼痛、腰痛、骨节疼痛、怕风、无汗且喘息的症状，这是伤寒，用麻黄汤主治。太阳病，出现头痛、发热、出汗、怕风的症状，这是中风，用桂枝汤主治。虽然有伤寒六七天不大便，头痛且有发热的情况，给予调胃承气汤泻下治疗的记载；又有人说，如果小便清长，就知道热邪不在里，仍在表，应当给予桂枝汤。因为头痛未去，虽然六七天不大便，只要小便清长，仍然属于表证，由此可知头痛属于表证是明确的。
头痛一概归属于三阳经吗？阴经生病也有头痛吗？太阴经和少阴经的脉气，都上行至颈部和胸部后返回，不向上循行经过头部，所以很少有头痛的症状。只有厥阴经的脉气，沿着喉咙后面，上行进入颃颡（鼻咽部），连系目系，上行出额部，与督脉会合于头顶。厥阴经生病也会有头痛。医经说：“干呕、吐涎沫”的病症，用吴茱萸汤主治，指的就是这种情况。
头是精明之府，神明居住的地方。轻微邪气引起的头痛，可以通过发散法治疗。如果疼痛剧烈，牵连到脑部，并且手足寒冷，这又是真脏气受损的重病，难道还能仅仅用发散法治疗吗？唉，头痛虽然是外感疾病，尚且有不可治愈的情况，更何况是脏腑内部的疾病呢？
Headache in Cold Damage. How shall this be elucidated? Headache refers to the condition caused by pathogenic factors on the exterior meridians attacking upwards to the head. The *Nan Jing* (Classic of Difficult Issues) states: When the Three Yang Meridians are affected by Wind-Cold, which remain latent and do not depart, it is called Jue Headache (Jue Tou Tong). This indicates that the meridians of the Three Yang ascend to the head. However, in Cold Damage, headache is primarily governed by the Taiyang (Greater Yang) Meridian. Why? Because the Taiyang Meridian originates at the inner canthus of the eye, ascends to the forehead, intersects at the vertex, and enters to connect with the brain. The classics state that when the Taiyang Meridian is diseased, there is pain in the head and nape, and stiffness in the lower back and spine. It is also stated that after seven days, as the disease declines, the headache subsides slightly. Although both the Yangming (Yang Brightness) and Shaoyang (Lesser Yang) meridians present with headache, they do not govern it exclusively as the Taiyang does. Generally, Taiyang disease belongs to the Exterior syndrome, and headache serves specifically as a marker for Exterior syndromes. Regardless of whether the pathogen is Wind or Cold, resolution requires dispersing methods (diaphoresis).
In Taiyang disease, if there is headache, fever, body ache, low back pain, bone and joint pain, aversion to wind, absence of sweating, and wheezing, it is Cold Damage, treated with Mahuang Tang (Ephedra Decoction). In Taiyang disease, if there is headache, fever, sweating, and aversion to wind, it is Wind Strike, treated with Guizhi Tang (Cinnamon Twig Decoction). There are cases where, despite six or seven days of constipation in Cold Damage, headache and fever persist; in such instances, Tiaowei Chengqi Tang (Regulate the Stomach and Purge Decoction) may be used to purge. It is also said that if urination is clear, one knows the heat is not in the Interior but remains in the Exterior, and thus Guizhi Tang should be administered. Since the headache has not resolved, even with several days of constipation, if urination is clear, it still indicates an Exterior pattern. Thus, it is clear that headache belongs to the Exterior.
Is all headache attributed to the Three Yang Meridians? Can Yin meridians present with headache? The meridians of the Taiyin (Greater Yin) and Shaoyin (Lesser Yin) ascend to the neck and chest and then return; they do not ascend along the head. Therefore, these meridians rarely present with headache. Only the Jueyin (Terminal Yin) meridian follows the posterior aspect of the throat, ascends into the pharynx (hangsang), connects with the eye system, ascends out of the forehead, and meets the Du Mai (Governing Vessel) at the vertex. Disease of the Jueyin meridian can also cause headache. The classics state that for dry vomiting and spitting of saliva, Wuzhuyu Tang (Evodia Decoction) is indicated; this refers to such cases.
The head is the mansion of the spirit and clarity, where the Shen (Spirit) resides. For minor pathogenic factors causing headache, dispersing methods are appropriate. However, if the pain is severe, radiating to the brain, accompanied by cold hands and feet, it constitutes a critical disease involving the True Qi. Can it be treated merely by dispersing methods? Alas, although headache is an external ailment, there are incurable cases; how much more so for diseases of the Zang-Fu organs!