逆者，四肢逆而不温也，厥者，冷也，又甚于逆。四肢者，诸阳之本，常宜和
暖，如指头微寒者，阳气衰也（阳气起于十指之端），足心冷者，阴气胜也（阴脉集于足下而趣于足心）。
如疮本焦黑，烦渴顿闷，喘促而厥逆者，此阳毒内陷，热气逆伏，手足为之冷，所谓热深厥亦深，火极似水者。
如疮本灰白，泄利而厥逆者，此元气虚惫，阴阳不相顺接，而手足为之冷也。疮疹之候，头常欲凉，足常欲温，故
头温足冷者不治。厥逆乃疮家恶证也。
如因热深而厥者，大便不通，三乙承气汤（便闷）主之。疮黑者，百祥丸、牛李膏主之（俱见黑陷）。如因泄
利气虚而厥者，陈氏木香散（泻）、异功散（出不快）主之。但十指头微寒者，四君子汤（不能食）理中汤（吐利）并加
桂主之。痘疮发热，手足却宜和暖，虽云足属肾，要凉，凉非冷也，只与常人同，遍身皆热，而此同常人，故称
凉，亦和暖之意，非真冷也。若手足冷，由其人曾多吐泻，脾脏虚怯，脾主四肢，所以冷，冷为恶候，不可单用发
表，反损脾胃，宜和中、发表兼用。痘出以脾胃为主，又宜急与术作汤以饮之，不可因循空谈废事也，先以黄 建
中汤（腹痛）加防风、羌活，或四君子汤加黄 、桂枝、防风以发之，发后以四君子汤加黄 、白芍药、当归、桂
心以补脾胃，养气血，而助痘疮之成就也。
如疮始出，手足便冷者，其人先有吐利，四肢者皆禀气于胃，脾胃气弱，不得
至经，理中汤加桂主之。
参附汤 治痘疹阳气虚寒，切牙寒战，手足并冷，或吐泻不食，饮沸汤不知热，用独参汤加好真附，
炮如法者，每剂先加一钱，未应多加之，更不应，加至四五钱，或等分亦无妨，但用之以运其阳气，如已脱者，不治。
二神散 治伤冷体寒，肢冷腹痛，口气冷，难发难壮，暂用。
丁香（九粒） 干姜（一钱，煨）
上为末。每服五分，白汤送下。盖被片时，令脾胃温暖，阴反阳回，则痘变顺矣，量儿大小轻重用之。
所谓“逆”，是指四肢逆冷而不温暖；所谓“厥”，是指寒冷，其程度比“逆”更严重。四肢是诸阳经的根本，应当保持和暖。如果手指头微微发寒，说明阳气衰弱（阳气起始于十个手指的末端）；如果脚心寒冷，说明阴气偏胜（阴脉汇聚于足下并趋向足心）。
如果疮疹原本颜色焦黑，患者突然感到烦躁、口渴、神志昏闷，呼吸急促且出现厥逆症状，这是阳毒内陷，热气郁伏，导致手足变冷，这就是所说的“热深厥亦深”，即火极似水的表现。
如果疮疹原本颜色灰白，伴有腹泻且出现厥逆，这是元气虚弱疲惫，阴阳之气不能相互顺接，从而导致手足变冷。在疮疹的证候中，头部通常希望凉爽，足部通常希望温暖，所以如果头部温热而足部寒冷，属于不治之症。厥逆是疮家（患疮疹者）的危重证候。
如果是因热邪深重导致的厥逆，伴有大便不通，主治方剂为三乙承气汤（适用于大便闷滞的情况）。如果疮色发黑，主治方剂为百祥丸、牛李膏（均见于黑陷证的论述中）。如果是因腹泻、气虚导致的厥逆，主治方剂为陈氏木香散（适用于泄泻）、异功散（适用于痘出不畅）。如果只是十个手指头微微发寒，可用四君子汤（适用于食欲不振）或理中汤（适用于呕吐泄泻）并加入桂枝来主治。痘疮发热时，手足应当保持和暖，虽然常说足部属肾，应当凉爽，但这里的“凉”并非指“冷”，而是与常人相同，全身都热，唯独此处与常人一样，所以称为“凉”，这也是和暖的意思，并非真正的寒冷。如果手足冰冷，是因为患者之前有过多次吐泻，导致脾脏虚弱怯弱，脾主四肢，所以会发冷。手足冷是恶候，不可单独使用发汗解表的方法，否则会反而损伤脾胃，应当采用调和脾胃与解表兼用的方法。痘疮的治疗以脾胃为主，又应当急忙用白术煎汤给患儿服用，不可因循守旧、空谈误事。先使用黄芪建中汤（适用于腹痛）加入防风、羌活，或者四君子汤加入黄芪、桂枝、防风来发散邪气；发散之后，再用四君子汤加入黄芪、白芍药、当归、桂心来补益脾胃，滋养气血，从而帮助痘疮成熟痊愈。
如果疮疹刚发出，手足就立即变冷，说明患者先前已有吐利症状。四肢的气血都禀受于胃，如果脾胃气弱，气血无法到达经脉，主治方剂为理中汤加入桂枝。
参附汤：治疗痘疹阳气虚寒，表现为咬牙寒战，手足俱冷，或者呕吐泄泻、不能进食，喝热水也不知道烫手。用法是用独参汤加入优质的真附子，炮制方法要规范。每剂药先加一钱附子，如果没有效果再增加剂量，如果仍然没有效果，可加至四五钱，或者人参附子等量使用也无妨。但此药仅用于运化阳气，如果阳气已经脱失，则无法救治。
二神散：治疗因受寒导致的体质虚寒，肢体寒冷、腹痛，口气冷，痘疹难以发出、难以壮盛，暂时使用此方。
药材：丁香（九粒）、干姜（一钱，煨制）。
将上述药物研为细末。每次服用五分，用温水送服。盖上被子片刻，使脾胃温暖，阴退阳回，则痘疹变为顺证。用量根据患儿的大小和病情轻重而定。
"Ni" (counterflow) refers to the coldness and lack of warmth in the four limbs; "Jue" (extremity cold) refers to coldness, which is more severe than "Ni". The four limbs are the root of all Yang meridians and should normally be warm. If the fingertips are slightly cold, it indicates a deficiency of Yang Qi (Yang Qi originates from the tips of the ten fingers); if the soles of the feet are cold, it indicates an excess of Yin Qi (Yin meridians converge at the soles and trend towards the sole center).
If the rash was originally scorched black, and the patient suddenly experiences irritability, thirst, mental confusion, rapid breathing, and Jue Ni (counterflow extremity cold), this signifies the internal collapse of Yang Toxin and the stagnation of Heat Qi, causing the hands and feet to become cold. This is described as "the deeper the heat, the deeper the Jue," or fire appearing like water due to extreme heat.
If the rash was originally grayish-white, accompanied by diarrhea and Jue Ni, this indicates exhaustion of Yuan Qi (Original Qi) and the failure of Yin and Yang Qi to connect smoothly, resulting in cold hands and feet. In the manifestations of rashes, the head is typically desired to be cool, and the feet to be warm. Therefore, if the head is warm but the feet are cold, it is considered incurable. Jue Ni is a malignant syndrome in patients with rashes.
For Jue caused by deep-seated Heat, accompanied by constipation, the primary formula is Sanyi Chengqi Tang (Three-Yi Cathartic Decoction) [indicated for abdominal fullness/stool retention]. For black-colored rashes, Baixiang Wan (Baixiang Pill) and Niuli Gao (Niuli Paste) are indicated (both discussed under Black Collapse). For Jue caused by diarrhea and Qi deficiency, Chen's Muxiang San (Chen's Costus Powder) [indicated for diarrhea] and Yigong San (Yigong Powder) [indicated for poor eruption] are indicated. If only the fingertips are slightly cold, Sizijunzi Tang (Four Gentlemen Decoction) [indicated for anorexia] or Lizhong Tang (Regulate the Middle Decoction) [indicated for vomiting and diarrhea], both added with Guizhi (Cinnamon Twig), are used. During fever from smallpox/rash, the hands and feet should remain warm. Although it is said that the feet belong to the Kidney and should be cool, this "coolness" does not mean "cold"; it means being consistent with normal people—while the whole body is hot, the feet are merely normal/warm, hence termed "cool," implying warmth rather than true cold. If the hands and feet are cold, it is because the patient previously suffered frequent vomiting and diarrhea, leading to Spleen deficiency and weakness. Since the Spleen governs the four limbs, they become cold. Cold extremities are a bad omen; one must not use diaphoresis (sweating method) alone, as this would damage the Spleen and Stomach. Instead, harmonize the middle and release the exterior simultaneously. Treatment of smallpox/rash focuses on the Spleen and Stomach; one should urgently administer decoctions made of Baizhu (Atractylodes Macrocephala Rhizome) for drinking. One must not procrastinate or engage in empty talk. First, use Huangjianzhong Tang (Huangjianzhong Decoction) [indicated for abdominal pain] added with Fangfeng (Saposhnikovia Root) and Qianghuo (Notopterygium Rhizome), or Sizijunzi Tang added with Huangqi (Astragalus Root), Guizhi (Cinnamon Twig), and Fangfeng to disperse the pathogen. After dispersion, use Sizijunzi Tang added with Huangqi (Astragalus Root), Shaoyao (Peony Root), Danggui (Angelica Sinensis Root), and Guixin (Cinnamon Heart) to tonify the Spleen and Stomach, nourish Qi and Blood, and assist in the maturation of the rash.
If the hands and feet become cold immediately upon the emergence of the rash, it indicates prior vomiting and diarrhea. The Qi of the four limbs is derived from the Stomach; if Spleen and Stomach Qi is weak, it cannot reach the meridians. Lizhong Tang (Regulate the Middle Decoction) added with Guizhi (Cinnamon Twig) is indicated.
Shenfu Tang (Ginseng and Aconite Decoction): Treats Yang Qi deficiency and cold in smallpox/rash, characterized by teeth chattering, rigors, cold hands and feet, vomiting, diarrhea, anorexia, and insensitivity to heat when drinking boiling water. Use Dushen Tang (Single Ginseng Decoction) added with high-quality Zhen Fuzi (Prepared Aconite Lateral Root), processed according to standard methods. Add 1 qian of Fuzi per dose initially; if ineffective, increase the dose. If still ineffective, increase to 4-5 qian, or use equal parts of Ginseng and Aconite. However, this is only used to circulate Yang Qi; if Yang Qi has already collapsed, it is untreatable.
Ershen San (Two Gods Powder): Temporarily used for cold injury and constitutional cold, manifesting as cold limbs, abdominal pain, cold breath, and difficulty in eruption and strengthening of the rash.
Ingredients: Dingxiang (Caryophylli Flos, 9 grains), Ganjiang (Zingiberis Rhizoma, 1 qian, roasted).
Grind into powder. Take 0.5 fen each time, washed down with warm water. Cover with a blanket for a period to warm the Spleen and Stomach, allowing Yin to retreat and Yang to return, thus transforming the rash into a favorable course. Dosage should be adjusted according to the child's age and severity.