汗者，水也，肾之所主也。内藏则为液，上升则为津，下降则为尿，外泄则为
汗。而所以外泄，则火之所蒸发也。火属心，故谓汗为心之液。火盛者，虽表固亦
出；不盛者，必表疏乃出。自汗者，非因发表而汗自出也，其出无时，火退乃
已。伤风伤寒，皆热蒸汗出，中暑病湿亦然。五志过极则生火，亦汗出。（如惊则心神浮
动飞越，汗随出可见。）劳动则生火，饮食则长气，（《经》云∶食入于阴，长气于阳。
气属于阳，气有
余便是火也。）房事则精泄于下，火散于上，故皆汗出。火在里，则汗随脏腑出；火
在表，则汗从经脉出。（如太阳伤风，热在皮肤，则翕翕汗出，乃肌表之汗也。阳明
胃实，则蒸蒸汗出，乃
胃府之汗也。翕翕、蒸蒸皆热貌，翕字为合羽，其身如合羽所覆，扪之自温；蒸蒸则如炊
笼腾越，扪之热气透手也。）
春夏气浮，汗出肌肤。秋冬气沉，汗出骨髓，故筋骨之疾宜汗者，当于冬至后发之。
自汗，旧云表虚，然不可概论。如伤寒其始无汗，后传阳明即自汗，岂前者表实，
后者表虚乎？（前之无汗，则阴邪凝固使然，无论其人平素表实无汗，即表虚亦无汗。
后传阳明，热盛蒸越，无
论其人平素表虚有汗，即表实亦有汗。问∶太阳伤风有汗，用桂枝汤，非表虚乎？曰；
伤风有汗，有汗则表疏，故
谓之虚。是因有汗而表虚，非因表虚而有汗也。因表虚而有汗，则重实表；因有汗而表虚，
则重散热。其用桂枝，
是发散风邪，非固表也，固表乃其兼能耳。）有实火，有虚火，阳虚，（即东垣补中益气证。）
阴虚，（即血
虚。）肾阳虚，肾阴虚，皆发热，皆虚火也。火炎则身温汗热而肤涩，阳虚则身凉汗冷
而肤滑。（阳衰则卫气不固，又阳虚则不能内守，而易于浮越也。然亦有热极而反出冷汗者，
盖热聚于内，肌肤反
冷，肤冷故汗亦冷也。或汗过多，阳从汗脱所致。然热甚汗多而脱者，其汗必先热，后
乃冷耳。丹溪谓热极反汗冷，乃
火盛兼水化，其说牵强。）盗汗者，寤时无汗，寐时汗出，如盗乘人睡熟而出也。人寤则气
行于阳，寐则气行于阴。若其人表阳虚者，遇寐而气行于里之时，则表更失所护而
益疏，即使内火不盛，而阳气团聚于里，与其微火相触发，亦必汗出。若内火素盛，
两阳相搏，阴液被扰，虽表固者，亦必溃围而出矣。（其人阴虚尤易动。）及其醒觉，则阳
气还出于表，而汗自止。伤寒之盗汗亦然，盖邪在半表半里时，寤则气挟邪还于表，
阴得安静不扰，故无汗；寐则气挟邪入于里，阴被扰而不宁，故汗出也。（丹溪谓杂证之
盗汗，有阳虚，有阴虚，大病后阴气未复，遗热未清，或劳役、七情、色欲之火，或饮食积热，
皆足耗损精血。阴
气既伤，阳火独旺，内蒸成汗也。）
心孔汗，别处无汗，独心孔一处有汗。由思虑过多，心神浮越使然。头汗，别
处无汗，热不得外越，但上蒸也。或因黄郁未发，或因湿家误下，或因水结胸蒸，
或因火劫热迫，或因阳明蓄血，或因热入血室，并详《伤寒论》。手足汗，别处无
汗，脾胃之热达于四肢也。（脾胃主肌肉、四肢，热达于肌肉则体汗，若达于四肢则手足汗耳。）冬月足
多汗，气降也。又有手足汗，属脾胃虚寒，不能营运津液，乘虚阳外越，（虚阳
被寒所逼外越。）而横溢于四肢者。如阴盛而淫雨滂沱，其汗必冷，与实热之汗（其汗必热
）不同。
脱汗。阴盛格阳，汗从阳脱，味淡不咸，（久藏之液则咸，若才经气化之液则淡，
咸者已经出
尽，并新化之液亦出，则津随气脱可知矣。）如珠不流，（无继故也。为绝汗，）不治。
（淋漓如雨，拭揩不及，
及液涸而火正炎，熬煎如胶之粘者，皆难治。）
汗，本质是水液，由肾脏所主管。在体内贮藏时称为“液”，向上输布则成为“津”，向下排泄则变成尿液，向外渗出则形成汗。而之所以能向外渗出，是因为受到火的蒸腾作用。火归属于心，因此称汗为“心之液”。如果火势旺盛，即使体表闭塞也会出汗；如果火势不旺，必须体表疏松才会出汗。自汗，是指并非因为使用发汗药而自然出汗，出汗没有固定时间，直到火气消退才停止。伤风、伤寒，都是因热邪蒸腾导致出汗，中暑和湿病也是如此。七情（喜、怒、忧、思、悲、恐、惊）过度则会化火，也会导致出汗。（例如惊恐会使心神浮动散乱，汗随之而出，由此可见。）劳动会产生火，饮食会助长阳气，《内经》说：“食物进入阴分，会在阳分产生气。”气归属于阳，阳气有余就是火。房事会导致精气在下部泄露，火气在上部散发，所以都会导致出汗。火在体内，汗就随脏腑的表现而出；火在体表，汗就从经脉而出。（例如太阳经伤风，热邪在皮肤，表现为微微出汗，这是肌表的汗。阳明胃腑实证，表现为蒸蒸大汗，这是胃府的汗。“翕翕”、“蒸蒸”都是形容热的样子，“翕”字意为合羽，身体像被羽毛覆盖一样，摸上去温热；“蒸蒸”则像蒸笼热气腾腾，摸上去热气透手。）
春夏季节，阳气浮越，汗出在肌肤。秋冬季节，阳气沉降，汗出在骨髓，所以对于筋骨疾病需要发汗治疗的，应当在冬至之后进行。
自汗，过去常说属于表虚，但不能一概而论。例如伤寒初期无汗，后来传入阳明经就出现自汗，难道前期是表实，后期就是表虚吗？（前期的无汗，是阴邪凝固所致，无论病人平时是表实无汗还是表虚无汗，此时都无汗。后期传入阳明，热盛蒸腾外越，无论病人平时是表虚有汗还是表实无汗，此时都有汗。问：太阳经伤风有汗，用桂枝汤治疗，难道不是表虚吗？答：伤风有汗，因为有汗所以体表疏松，因此称之为虚。这是因为有了汗才导致体表疏松，而不是因为体表疏松才导致有汗。如果是因体表疏松而有汗，治疗应重在固表；如果是因有汗导致体表疏松，治疗应重在散热。使用桂枝，是为了发散风邪，并非为了固表，固表只是它的兼带功效。）有实火，有虚火，阳虚（即李东垣所说的补中益气证），阴虚（即血虚），肾阳虚，肾阴虚，都会发热，都属于虚火。火炎上则身体温暖、汗热且皮肤干燥涩滞；阳虚则身体凉爽、汗冷且皮肤滑润。（阳气衰微则卫气不固，另外阳虚则不能在内守持，而易于浮越。然而也有热极反而出冷汗的情况，这是因为热邪聚集在体内，肌肤反而寒冷，皮肤冷所以汗也冷。或者是汗出过多，阳气随汗脱失所致。然而热甚汗多导致脱证的，其汗必然是先热后冷。朱丹溪认为热极反而出冷，是火盛兼有水化，这种说法牵强附会。）盗汗，是指清醒时无汗，睡眠时出汗，就像盗贼趁人熟睡时出来一样。人清醒时，气行于阳分；睡眠时，气行于阴分。如果此人表阳虚，遇到睡眠时气行于里的时刻，则体表更加失去护卫而更加疏松，即使内火不旺盛，但阳气团聚于里，与微弱的火气相互触发，也一定会出汗。如果此人内火素来旺盛，两阳相搏，阴液被扰动，即使体表坚固，也必定冲破束缚而出汗。（此人阴虚尤其容易动。）等到醒来，阳气回到体表，汗自然停止。伤寒病的盗汗也是如此，大概是因为邪气在半表半里之间，清醒时气挟带邪气还于体表，阴分得到安静不被扰乱，所以无汗；睡眠时气挟带邪气进入体内，阴分被扰动而不安宁，所以出汗。（朱丹溪认为杂病的盗汗，有阳虚的，有阴虚的，大病后阴气未恢复，余热未清，或者劳役、七情、色欲之火，或者饮食积热，都足以耗损精血。阴气既已受伤，阳火独旺，在内蒸腾形成汗。）
心孔汗，别处无汗，只有心口一处有汗。这是由于思虑过多，心神浮越所致。头汗，别处无汗，热邪不能向外发散，只能向上蒸腾。可能是因为黄疸郁结未发，可能是因为湿病患者误用下法，可能是因为水饮结聚胸膈蒸腾，可能是因为火劫法迫使热邪外出，可能是因为阳明蓄血，可能是因为热入血室，这些在《伤寒论》中都有详细说明。手足汗，别处无汗，是脾胃的热邪达于四肢所致。（脾胃主肌肉和四肢，热邪达于肌肉则全身出汗，若达于四肢则只有手足出汗。）冬季足部多汗，是气机下降的缘故。又有手足汗，属于脾胃虚寒，不能运化输送津液，乘虚阳外越（虚阳被寒邪逼迫外越），而横溢于四肢。如阴气盛而淫雨滂沱，其汗必然冷，这与实热之汗（其汗必然热）不同。
脱汗。阴盛格阳，汗从阳分脱失，味道淡而不咸。（久藏的体液是咸的，若是刚经过气化作用的体液则是淡的，咸味的是已经排尽的，连同新气化的体液也一起排出，则可知津液随气脱失。）汗珠如珍珠状但不流动（因为没有后继之汗，称为绝汗），难以治愈。（淋漓如雨，擦拭不及，以及津液枯竭而火正旺，煎熬得像胶一样粘稠的，都难治。）
Sweat is essentially water, governed by the Kidney. When stored internally, it is called "Ye" (thick fluid); when ascending, it becomes "Jin" (thin fluid); when descending, it turns into urine; and when exuding externally, it forms sweat. The reason for external exudation is evaporation by Fire. Fire belongs to the Heart, thus sweat is referred to as the "fluid of the Heart." If Fire is vigorous, sweat will occur even if the exterior is closed; if Fire is not vigorous, sweat occurs only when the exterior is loose. Spontaneous sweating refers to sweating naturally without the use of diaphoretic agents; it occurs at any time and ceases only when the Fire subsides. Wind-stroke and Cold damage both involve heat steaming causing sweat, as do Summerheat and Dampness diseases. Extreme excess of the Five Emotions generates Fire, also leading to sweating. (For instance, fright causes the Heart Spirit to float and scatter, with sweat following, which demonstrates this.) Labor generates Fire, and diet nourishes Qi. (*Classic of Acupuncture and Moxibustion* states: "Food enters the Yin, generating Qi in the Yang." Qi belongs to Yang; excess Qi constitutes Fire). Sexual activity causes Essence to leak below and Fire to dissipate above, thus all lead to sweating. If Fire is internal, sweat follows the Zang-Fu organs; if Fire is external, sweat issues from the meridians. (For example, in Taiyang wind-strike, heat is in the skin, presenting as slight sweating, which is sweat of the muscle-surface. In Yangming stomach excess, there is steaming profuse sweating, which is sweat of the Stomach organ. "Xi Xi" and "Zheng Zheng" both describe heat. "Xi" means covering feathers; the body feels warm like being covered by feathers. "Zheng Zheng" is like steam rising from a steamer, feeling hot to the touch.)
In Spring and Summer, Qi floats, and sweat appears on the skin and muscles. In Autumn and Winter, Qi sinks, and sweat relates to the bones and marrow. Therefore, for bone and joint conditions requiring sweating therapy, it should be initiated after the Winter Solstice.
Spontaneous sweating was traditionally attributed to Exterior Deficiency, but this cannot be generalized. For instance, in Cold damage, there is initially no sweat, but upon transmission to Yangming, spontaneous sweating occurs. Does this mean the former was Exterior Excess and the latter Exterior Deficiency? (The initial lack of sweat is due to Yin pathogen coagulation; regardless of whether the person usually has an Exterior Excess or Deficiency constitution, there is no sweat then. Upon transmission to Yangming, Heat is vigorous and steams outward; regardless of whether the person usually has an Exterior Deficiency or Excess constitution, there is sweat then. Question: Taiyang wind-strike presents with sweat, treated with Guizhi Tang (Cinnamon Twig Decoction), isn't that Exterior Deficiency? Answer: Wind-strike with sweat implies the exterior is loose due to sweating, hence termed deficiency. This is because sweating leads to a loose exterior, not because a loose exterior causes sweating. If sweating is caused by a loose exterior, treatment should focus on consolidating the exterior. If a loose exterior results from sweating, treatment should focus on dissipating heat. Using Guizhi (Cinnamon Twig) is to disperse Wind pathogens, not primarily to consolidate the exterior; consolidation is merely a secondary effect.) There are Excess Fire and Deficient Fire. Yang Deficiency (i.e., Li Dongyuan's Bu Zhong Yi Qi syndrome), Yin Deficiency (i.e., Blood Deficiency), Kidney Yang Deficiency, and Kidney Yin Deficiency all cause fever and belong to Deficient Fire. Fire flaring up results in warm body, hot sweat, and dry/rough skin. Yang Deficiency results in cool body, cold sweat, and smooth skin. (Yang decline leads to insecure Wei Qi; additionally, Yang Deficiency fails to hold inward, making it prone to floating outward. However, extreme Heat can paradoxically produce cold sweat. This is because Heat aggregates internally, making the skin cold, thus the sweat is cold. Or, excessive sweating causes Yang to escape with the sweat. In cases of severe Heat and profuse sweating leading to collapse, the sweat must first be hot before becoming cold. Zhu Danxi's theory that extreme Heat reverses to cold sweat, attributing it to Fire excess combined with Water transformation, is forced.) Night sweating refers to no sweat while awake, but sweating during sleep, like a thief acting while one sleeps. When awake, Qi moves in the Yang; when asleep, Qi moves in the Yin. If a person has Exterior Yang Deficiency, when sleeping and Qi moves inward, the exterior loses protection and becomes looser. Even if internal Fire is not vigorous, the Yang gathering internally triggers the slight Fire, causing sweat. If internal Fire is inherently vigorous, the two Yangs clash, disturbing Yin fluids; even with a firm exterior, sweat will break through. (Those with Yin Deficiency are especially prone to this.) Upon waking, Yang returns to the exterior, and sweat stops. Night sweating in Cold damage is similar: when pathogens are in the Half-Exterior/Half-Interior, waking allows Qi to carry pathogens back to the exterior, allowing Yin to rest undisturbed, so no sweat; sleeping allows Qi to carry pathogens inward, disturbing Yin, so sweat occurs. (Zhu Danxi stated that night sweating in miscellaneous diseases can be due to Yang Deficiency or Yin Deficiency. After major illness, if Yin Qi is not restored and residual heat remains, or due to labor, emotions, sexual desire, or dietary stagnation heat, all consume Essence and Blood. Once Yin is damaged, Yang Fire burns alone, steaming internally to form sweat.)
Heart-pore sweating involves sweat only at the heart region, nowhere else. It is caused by excessive thinking leading to the floating and scattering of the Heart Spirit. Head sweating involves sweat only on the head, where Heat cannot vent outward and steams upward. Causes include unresolved Jaundice dampness, mistaken purgation in Dampness patients, Water accumulation in the chest steaming, Heat forced by fire therapy, Yangming blood stasis, or Heat entering the Blood Chamber, all detailed in *Shanghan Lun*. Hand and foot sweating involves sweat only on hands and feet, indicating Spleen/Stomach Heat reaching the limbs. (The Spleen and Stomach govern muscles and limbs; Heat reaching muscles causes general sweating, while Heat reaching limbs causes hand/foot sweating.) Foot sweating in winter is due to Qi descending. Another type of hand/foot sweating belongs to Spleen/Stomach Deficient Cold, failing to transport fluids, allowing Deficient Yang to escape outward (forced out by Cold) and overflow into the limbs. Like heavy rain during Yin abundance, this sweat is cold, differing from Excess Heat sweat (which is hot).
Collapse sweating. Yin excess repels Yang, causing sweat to escape via Yang. The taste is bland, not salty. (Long-stored fluids are salty; freshly qi-transformed fluids are bland. Salty indicates old fluids exhausted, and new fluids escaping too, showing Jin-Ye escaping with Qi.) Sweat beads like pearls but does not flow (due to lack of subsequent sweat, known as "Jue Han" / Absolute Sweat), untreatable. (Profuse sweating like rain, unable to wipe dry, or fluids exhausted with Fire blazing, boiling like sticky glue, are all difficult to treat.)