Explanation and Common Knowledge of Sanfu Days
Sanfu days occur between Minor Heat and Major Heat, representing the hottest, most humid, and muggy time of the year. The term "Fu days" refers to the "Sanfu days" according to the lunar calendar, which is the hottest period of the year. It can be understood this way: "Fu" means the weather is so hot that one should stay still rather than move. However, the reason it is called "Fu" is also because there are significant cold factors involved. Sanfu refers to the hottest thirty to forty days of the year in the Central Plains region. It is calculated based on the lunar calendar, generally falling between mid-July and early-August in the Gregorian calendar.
Explanation of "Fu"
Classically, "Fu" means to lie dormant. The "Fu" in "Sanfu days" refers to "pathogenic heat." It is the "summer heat" pathogen, one of the "Six Evils" (referring to "wind, cold, summer heat, dampness, dryness, and fire"). In summer, this summer heat pathogen gradually lies deep within the body without being noticed. If it is not removed, in autumn, the fire pathogen overcomes the metal pathogen, damaging the lung qi, which leads to a weakened immune system and diseases like colds, coughs, and fever. Then, in winter, these illnesses will recur repeatedly. "In autumn, one may suffer from intermittent fevers and malaria, with little benefit for the autumn harvest, and the illness worsens at the winter solstice."
Therefore, the *Huangdi Neijing* (The Yellow Emperor's Inner Canon) clearly advises to "allow qi to be discharged, as if you were fond of being outdoors." Do not hide in an air-conditioned room for fear of sweating. Cold drinks not only fail to dispel summer heat but can also harm the spleen and stomach. It should be known that tea is the best drink for relieving summer heat. Although drinking a cup of hot tea will make you sweat, it is followed by a wave of coolness. One must not only consider the immediate situation but should look further ahead. Health cultivation must begin in the present.
Entering Fu
The time of entering Fu each year is not fixed, nor is the length of the mid-Fu period the same. It needs to be calculated by consulting an almanac. Simply, the date of entering Fu can be expressed by the four-character mnemonic "Xiazhi Sangeng," which means starting from the third "Geng" day after the Summer Solstice. The first Fu is 10 days, the mid-Fu is 10 or 20 days, and the last Fu is 10 days. Ancient China used the "Ganzhi system" for recording days, consisting of 60 different combinations of the ten Heavenly Stems and twelve Earthly Branches, used in a cycle. Days with the character "Geng" are called "Geng" days. The "Geng" character is the 7th of the ten Heavenly Stems: "Jia, Yi, Bing, Ding, Wu, Ji, Geng, Xin, Ren, Gui." A "Geng" day repeats every 10 days. Starting from the Summer Solstice, according to the Ganzhi sequence, the third "Geng" day is the first Fu, the fourth "Geng" day is the mid-Fu, and the first "Geng" day after the Start of Autumn is the last Fu. When there are four "Geng" days between the Summer Solstice and the Start of Autumn, the mid-Fu is 10 days; when there are five, it is 20 days. It seems that the timing of the "Geng" days affects the length of the mid-Fu, which is why some years have 30-day Fu periods and others have 40-day Fu periods.
Calculation
Each Fu period is 10 days, calculated according to the ten Heavenly Stems. Therefore, the division of Sanfu days is as follows: the third "Geng" day after the Summer Solstice marks the beginning of the first Fu. For example, in 2006, the Summer Solstice was June 21st in the Gregorian calendar, and the Heavenly Stem of that day was "Xin." 28 days later is the third "Geng" day, so July 20, 2006, was the start of the first Fu. Ten days later, another "Geng" day, July 29th, marks the beginning of the second Fu. Ten days later, another "Geng" day, which is also the first "Geng" day after the Start of Autumn, August 9th, marks the beginning of the third Fu. If it were 2007, July 15th would be the third "Geng" day, marking the start of the first Fu (Chu Fu). Ten days later, another "Geng" day, July 25th, marks the beginning of the second Fu (Zhong Fu). Ten days later, another "Geng" day, but the Start of Autumn has not yet passed. Ten more days later (making the mid-Fu 20 days this year), it is another "Geng" day, and the first "Geng" day after the Start of Autumn, which is August 14th, marks the beginning of the third Fu. This means that after entering Sanfu days each year, the weather is very hot, especially during the ten days of the third Fu, which are the hottest.
Reason for the Hottest Weather
After entering Fu, the surface humidity increases. The ground absorbs more heat each day but dissipates less, causing heat to accumulate. Thus, it gets hotter day by day. Upon entering Sanfu, the accumulated heat on the ground reaches its peak, making the weather the hottest. Additionally, summer brings heavy rainfall and high air humidity. The heat capacity of water is much greater than that of dry air, which is another important reason for the muggy weather. In July and August, the subtropical high-pressure system strengthens. Under its control, the sinking air currents within the high-pressure zone result in clear, cloudless weather, which is beneficial for sunlight exposure and ground radiation heating, making the weather even hotter.
Therapeutic Effects
Because Sanfu days are the period of the year with the hottest weather, highest temperatures, and most abundant yang qi, the body's pores are loose, and the meridians and qi and blood are flowing smoothly. This is conducive to the penetration and absorption of medicinal herbs. Furthermore, "Geng" days are related to the Lung Metal (Geng day belongs to Metal and is associated with the Large Intestine, which has an exterior-interior relationship with the Lung), making it the optimal time to warm the lung meridian's yang qi and expel internally hidden cold pathogens. Coupled with the careful selection of acupoints on the Bladder and Governor Vessels that have the effects of warming the meridians, dispelling cold, resolving phlegm, and calming wheezing for application, the effects are mutually reinforcing, achieving the goal of supporting the righteous qi and expelling pathogenic factors. Therefore, it can play a role in preventing and treating diseases.
Diet
Traditional Chinese Medicine (TCM) believes that "summer is characterized by heat and dampness, making it suitable for light tonification." The scorching heat of summer makes people fond of cold drinks and consuming more water, which can lead to dampness invading the body. External dampness entering the interior can cause water-dampness to stagnate in the spleen, disrupting the spleen and stomach's ascending and descending functions, leading to digestive problems, such as fluid retention and loss of appetite. Damp-heat is very detrimental to the spleen. Foods with a bitter taste have a drying effect and should not be consumed excessively. Therefore, daily diet should include more sweet and cool or sweet and cold foods. Moreover, summer corresponds to the Heart in the five elements, and the Heart prefers coolness and benefits from sour flavors. Thus, one should appropriately eat more sour foods in the summer. For example, one can regularly consume wheat products, plums, peaches, olives, pineapples, celery, etc. TCM emphasizes harmony between humans and nature and the balance of yin and yang. Therefore, in addition to eating more sour and sweet foods in the summer, one should try to avoid pungent, warm, and drying foods. It is also important to avoid excessive raw food and cold drinks, as they can damage the body's righteous qi and induce disease.