Cold and heat refer to the patient's subjective feeling of chills and fever. Inquiry about cold and heat means to ask the patient about sensations of heat and cold.

Present symptoms and signs constitute a main part of the history of any present illness. In TCM, pattern diagnosis is based on present symptoms and signs, and treatment is based on pattern differentiation.

Fever and cold are the common symptoms observed in the courses of many diseases and are the evidence for recognizing the nature of pathogenic factors and the state of yin and yang of the body. Fever pertains to yang while cold pertains to yin and each of them has subtypes*.

Fever refers to elevation of the body temperature above normal or a subjective feeling* of feverishness. This usually indicates that the body temperature regulatory set-point* has been raised by hyperactivity of yang or by the struggle between pathogenic factors and healthy qi.

Cold means feeling no warmth or feeling uncomfortably chilled. In some cases, when a person feels cold, he/she may shiver*, indicating a fierce struggle between external pathogenic factors and healthy qi. In some other cases, people may have reversal cold of the extremities*, suggesting yang qi failing to warm the extremities.

Generally speaking, pathogenic cold leads to a cold sensation and pathogenic heat leads to fever. Exuberance of yang leads to fever and exuberance of yin leads to cold, deficiency of yin brings about fever and deficiency of yang results in cold, as listed in Fig. 8-1.

A patient may feel cold and have fever simultaneously (cold with fever*), may only feel cold (chills without fever*), may only have fever (fever without chills*), or may have fever and cold alternatively (alternation of chills and fever*).

Cold with fever is usually caused by external contraction*, while cold without fever is mostly caused by internal damage* of body yang qi. Fever without chills is usually observed in internal heat patterns, caused by exuberance of yang or deficiency of yin.

High fever with aversion to heat* and without chills is usually observed in interior excess heat pattern.

Tidal fever* is a fever with periodic* rise and fall at fixed hours of the day like the morning and evening tides. Late afternoon tidal fever* is a fever more marked at 3-5 p. m. daily, usually due to the heat in yang brightness meridian*, also called yang brightness tidal fever. Dampness-warm tidal fever* is characterized by unsurfaced fever* worsening in the afternoon or evening, and often caused by dampness-heat retention in the middle energizer obstructing yang qi from spreading out. Yin deficiency tidal fever* is marked by fever in the afternoon (called afternoon tidal fever) or at night (named night fever). Vexing heat in the chest, palms and soles (also called five center fever*), and bone-steaming tidal fever* are characteristics of the fever caused by yin deficiency, and this fever is usually accompanied by flushed cheeks, night sweating*, dry mouth and throat as well as red tongue with scanty* fur.* Heat caused by deficiency of yin is called deficiency heat*.

Mild fever* refers to low-grade fever, mostly due to interior heat, and can be caused by qi deficiency, blood deficiency, dual deficiency of qi and yin, qi depression, or yin deficiency.

Alternating chills and fever* refers to chills without fever and fever without chills occurring in alternating succession, resulting from waxing and waning of pathogenic factor and healthy qi during their struggle. Alternating chills and fever with no fixed time is mostly observed in lesser yang disease*, a half-exterior half-interior pattern*. Alternating chills and fever with fixed time, such as alternating chills and fever once a day, once every two days, or once every three days, accompanied by severe headache, thirst and profuse sweating, is often observed in malaria*, brucella* and other infectious diseases.