《内经》曰∶诸燥枯涸，干劲皱揭，皆属于燥。乃阳明燥金，肺与太阳之气也，故曰燥
。万物莫 乎火，燥之为病，皆属燥金之化。然金体本燥，能令燥者火也。夫金为阴之主，
为水之源，而受燥气，寒水生化之源，竭绝于上，而不能灌溉周身，营养百骸，色干而无润
泽，皮肤滋生毫毛者，有自来矣。或大病而克伐太过，或吐利而亡津液，或预防养生，误饵
金石之药，或房劳致虚，补塞燥剂，食味过浓，辛热太多，醇酒炙肉，皆能偏助狂火，而损
害真阴，阴中伏火，日渐煎熬，血液衰耗，使燥热转甚为诸病，在外则皮肤皱揭，在上则咽
鼻焦干，在中则水液衰少而烦渴，在下则肠胃枯涸、津不润而便难，在手足则痿弱无力，在
脉则细涩而微，此皆阴血为火热所伤也。《原病式》云∶风热火同阳也。寒燥湿同阴也，又
燥湿小异也，燥金虽属秋阴，而异于寒湿，故反同其风热也。火热胜而金衰，而风生，则风
能胜湿，热能耗液而反寒，阳实阴虚，则风热胜于水湿而为燥也。凡人风病多因热甚而风，
燥者为其兼化，以热为其主也。然阳实阴虚，而风热太甚，以胜水湿，因而成燥，肝主于筋
，而风气自甚，又燥热加之，液还聚于胸膈，则筋太燥也。燥金主于收敛劲切，肾涩故为病
筋脉劲强，紧急而口噤也。或病燥热太甚，而脾胃干涸，而成消渴者，或风热燥甚，怫郁在
表，里气平者，善伸数欠，筋脉拘急，或时恶寒，或筋惕而搐，脉浮数而弦也，风热燥郁甚
于里，故烦满而或闭结也。及风痫之发作者，由热甚而风燥，为其兼化，涎溢胸膈，燥烁而
螈，昏冒僵仆也。凡此诸证，皆由热甚而生。风燥各有异者，由风热燥各微甚不等故也。
所谓中风或筋缓者，因其风热胜湿而为燥，乃燥之甚也。然筋缓不收而痿痹，故诸 郁病痿
，皆属肺金，乃燥之化也。如秋深燥甚，则草木痿落而不收，病之象也，是以手得血而能握
，足得血而能步。夫燥之为病，血液衰少，而气血不能通畅，故其病也，治法当以甘寒滋润
之剂，故甘寒俱能生血。又寒能胜热，阴得滋而火杀，液得润而燥除，源泉下降，精血上荣
，如是则气液宣通，由内神茂而外色泽矣。《内经》治法，燥者润之，非养血润燥之谓欤。
世或有言风热而燥，误以辛凉驱风苦泄之剂，愈燥其液，损之又损，殊不知血衰致燥，多招
风象，乃木火得侮金水之衰也。风燥之疾，当求其本，治则不失矣。
《黄帝内经》说：各种因干燥导致的干枯、收缩、僵硬和脱屑症状，都属于燥邪致病。这是阳明燥金之气，与肺和太阳经的气机相关，所以称为燥。万物没有不被火影响的，燥邪引起的疾病，都归属于燥金的化生。然而，金的本体本来就是燥的，能够导致人体变燥的是火。金是阴气的主宰，也是水的源头，如果受到燥气侵袭，作为寒水生化之源的上焦就会枯竭，无法灌溉全身，滋养骨骼肌肉，导致面色干枯而没有润泽，皮肤生长毫毛的现象也就有了由来。或者在大病之后攻伐太过，或者呕吐腹泻导致津液亡失，或者在预防养生时，误服金石类药物，或者因房劳导致虚弱，服用过于温补燥热的药物，饮食口味过重，辛辣热性食物过多，以及饮用烈酒、吃烤肉等，都能偏助狂躁之火，损害真阴。阴中潜伏的火气，日渐煎熬，导致血液衰耗，使燥热更加严重从而引发各种疾病。表现在外部则是皮肤皱缩脱屑，表现在上部则是咽喉鼻腔焦干，表现在中部则是水液减少而烦渴，表现在下部则是肠胃干枯、津液不润而导致大便困难，表现在手足则是痿弱无力，表现在脉象上则是细涩而微弱，这些都是因为阴血被火热所损伤。
刘完素在《原病式》中说：风、火、热同属阳；寒、燥、湿同属阴。但燥与湿略有不同，燥金虽然属于秋季的阴气，却不同于寒湿，反而与风热相似。当火热亢盛而金气衰弱时，风气就会内生，风能胜湿，热能耗伤津液从而反现寒象（此处指津亏之假寒或相对状态），导致阳实阴虚，风热胜过水湿而表现为燥证。凡是人的风病，多因热极生风，燥证往往是其兼夹变化，以热为主要因素。然而，由于阳实阴虚，风热太甚，胜过水湿，因而形成燥证。肝主筋，若风气过盛，又加上燥热侵袭，津液聚于胸膈而不能濡养四肢，则筋脉过于干燥。燥金主收敛劲切，肾气涩滞，故出现筋脉劲强、紧急且口噤的症状。或者因燥热太甚，脾胃干涸，而形成消渴病；或者因风热燥邪太甚，郁结在体表，若里气平和，则表现为喜欢伸展、频繁打哈欠，筋脉拘急，有时怕冷，有时筋肉跳动抽搐，脉象浮数而弦。若风热燥邪郁结在体内深处，则会出现烦闷胀满甚至便秘闭结。至于癫痫发作，是由于热极生风燥，为其兼夹变化，涎液溢于胸膈，燥热灼烁导致抽搐，神志昏迷、僵倒。所有这些证候，都是由热极而生。风燥各有不同的表现，是因为风、热、燥各自的轻重程度不等所致。所谓中风导致筋脉弛缓的，是因为风热胜湿而为燥，这是燥邪严重的表现。然而筋脉弛缓不收导致痿痹，所以各种郁病痿证，都归属于肺金，这是燥的化生表现。就像深秋燥气严重时，草木枯萎掉落而不收拢，这是疾病的征象。因此，手得到血的滋养才能握物，脚得到血的滋养才能行走。
燥邪引起的疾病，是因为血液衰少，气血不能通畅，所以治疗原则应当使用甘寒滋润的药物，因为甘寒都能生血。同时，寒能胜热，阴气得滋润则火气消退，津液得到润泽则燥邪去除，源泉下降，精血上荣，这样气液宣通，内在精神茂盛而外在色泽光泽。《黄帝内经》的治疗原则是“燥者润之”，难道不是指养血润燥的意思吗？世间有人说是风热致燥，错误地使用辛凉驱风、苦寒泄下的药剂，使得津液更加干燥，损伤又损伤，却不知道血衰导致燥证，容易招致风象，这是因为木火侮乘金水之衰败所致。对于风燥之疾，应当探求其根本，治疗原则就不会有失误了。
The *Huangdi Neijing* (Yellow Emperor's Inner Canon) states: "All conditions of dryness, withering, contraction, stiffness, and scaling belong to Dryness." This refers to the Qi of Yangming Dry Metal, associated with the Lung and Taiyang channels, hence termed Dryness. All things are influenced by Fire; diseases caused by Dryness belong to the transformation of Dry Metal. However, while Metal is inherently dry, it is Fire that causes the body to become dry. Metal is the master of Yin and the source of Water. If affected by Dryness Qi, the source of Cold Water's generation at the upper Jiao becomes exhausted, unable to irrigate the whole body and nourish the bones and muscles. This leads to a dry complexion lacking luster, explaining why hair grows on the skin. Such conditions arise from various causes: excessive purgation after severe illness, loss of Body Fluids due to vomiting or diarrhea, misuse of mineral drugs in preventive health care, deficiency induced by sexual exhaustion, use of overly warming and drying tonics, heavy flavors in diet, excessive spicy and hot foods, consumption of strong wine, and eating roasted meats. These factors can excessively assist raging Fire, damaging True Yin. The latent Fire within Yin gradually cauterizes, depleting Blood and causing Dry-Heat to intensify, leading to various diseases. Externally, this manifests as wrinkled and scaling skin; superiorly, as scorched and dry throat and nose; centrally, as decreased fluids causing irritability and thirst; inferiorly, as withered intestines and stomach, lack of lubricating fluids, and difficult defecation; in the limbs, as flaccidity and weakness; and in the pulse, as thin, choppy, and faint qualities. All these result from Yin-Blood being damaged by Fire-Heat.
Liu Wansu in the *Yuanbing Shi* (Treatise on the Causes of Diseases) states: Wind, Fire, and Heat are Yang; Cold, Dryness, and Dampness are Yin. Yet Dryness and Dampness differ slightly. Although Dry Metal belongs to Autumn Yin, it differs from Cold-Dampness and resembles Wind-Heat. When Fire-Heat prevails and Metal declines, Wind arises. Wind overcomes Dampness, and Heat consumes fluids, potentially creating a relative cold state, resulting in Excess Yang and Deficient Yin. Thus, Wind-Heat surpasses Water-Dampness, manifesting as Dryness. Most wind diseases stem from extreme Heat generating Wind; Dryness is often a concurrent transformation, primarily driven by Heat. Due to Excess Yang and Deficient Yin, if Wind-Heat is too severe and overcomes Water-Dampness, Dryness forms. The Liver governs the Tendons. If Wind is excessive and compounded by Dry-Heat, fluids gather in the chest and diaphragm rather than nourishing the extremities, causing the tendons to become overly dry. Dry Metal governs contraction and firmness; Kidney Qi becomes stagnant, leading to stiff and tense tendons, urgency, and lockjaw. Alternatively, extreme Dry-Heat may cause the Spleen and Stomach to become withered, resulting in Xiao Ke (Wasting-Thirst Syndrome). Or, if Wind-Heat-Dryness is severe and stagnates in the exterior, while interior Qi is balanced, symptoms include frequent stretching and yawning, tendon spasms, occasional aversion to cold, muscle twitching and convulsions, with a floating, rapid, and wiry pulse. If Wind-Heat-Dryness stagnates deeply in the interior, it causes irritability, fullness, and constipation. Epileptic seizures occur when extreme Heat generates Wind-Dryness as a concurrent transformation; saliva overflows into the chest and diaphragm, Dry-Heat cauterizes causing convulsions, and consciousness is lost with rigid collapse. All these syndromes arise from extreme Heat. Variations between Wind and Dryness depend on the differing degrees of severity among Wind, Heat, and Dryness. Stroke causing flaccid tendons occurs because Wind-Heat overcomes Dampness to create Dryness, representing severe Dryness. Flaccid tendons failing to retract lead to Wei Bi (Flaccidity and Obstruction Syndromes); thus, various stagnation-induced flaccidity syndromes belong to Lung Metal, reflecting Dryness transformation. Just as in late autumn, severe Dryness causes plants to wither and fall without retaining leaves, mirroring disease pathology. Hence, hands grasp only when nourished by Blood, and feet walk only when nourished by Blood.
Diseases of Dryness stem from depleted Blood and unsmoothed Qi and Blood circulation. Therefore, treatment should employ Sweet-Cold and moistening agents, as both Sweet and Cold properties generate Blood. Cold overcomes Heat; when Yin is nourished, Fire subsides; when fluids are moistened, Dryness is removed. The source descends, and Essence-Blood ascends to nourish. Consequently, Qi and fluids circulate freely, internal spirit flourishes, and external luster appears. The *Neijing* principle "Dryness should be moistened" implies nourishing Blood and moistening Dryness. Some mistakenly attribute Dryness to Wind-Heat, using Pungent-Cool wind-dispelling or Bitter-Draining formulas, which further dry the fluids and cause additional damage. They fail to realize that Blood deficiency leading to Dryness often attracts Wind manifestations, due to Wood-Fire insulting the deficiency of Metal-Water. For Wind-Dryness diseases, one must seek the root cause, ensuring the treatment principle remains correct.