Disease occurs, develops, and changes with the season, geography, climate variability, patient constitution, sex, age, lifestyle, and habit. Appropriate treatment is determined by a thorough knowledge of all aspects of the factors. For instance, the texture and interstitial space of the muscles differ with age and season.
The Basic Questions says, “Keep away from the cold climate when using the cold herbs; keep away from the warm climate when using the warm herbs; keep away from the hot climate when using the hot herbs”.
TCM believes each of the five Zang-viscera rises to prominence in its season. Liver-Qi dominates in spring, Heart-Qi in summer, Spleen-Qi in late summer, Lung-Qi in autumn, and Kidney-Qi in winter. According to the Five Elements principle, interrelationships among the five Zang-viscera in the seasons can be used to therapeutically select herbs. For example, when Liver-Qi dominates in spring, Spleen-Qi will be restricted. Therefore, Spleen deficiency must be treated by strengthening Spleen-Qi. Also, when Liver-Qi dominates in spring, it reinforces Heart-Qi, and therefore the syndrome of Heart-Qi deficiency can be more effectively treated in spring.
The constitution, the individual’s fundamental physical and mental makeup, is made up of Essence, Qi, and Spirit (in TCM, 
).Strong inherited Essence is the basis for a healthy life, and the foundation for the other two.
Physiological functions and the state of Qi and blood vary with sex, age, and constitution. Treatment and choice of herbs should account for these differences. At different ages people have different physiological and pathological characteristics. Men and women have physiological differences, and women’s health factors include menstrual disorders, leucorrhea, pregnancy, and delivery. The fetus may be harmed by extremely potent purgatives, extremely potent blood stasis removing herbs, lubricant herbs, or toxic herbs.
Patient constitution, strong or weak, Yin or Yang, cold or heat with pathological reaction following illness are also important factors. Different constitutions should be treated by different herbal formulas. Cold-natured herbs should be used very carefully with frequent Yang deficiency or dominant Yin.