Fever, Chills and Diarrhea in Sweltering Heat? Doctor Luo Dalun on Yin Shu (Summer-Heat Cold-Damp): the Hotter the Day, the Easier Cold-Damp Hurts You (Huo Xiang Zheng Qi · Zheng Chai Hu Yin · Fu Zi Li Zhong)

What people search for: yin shu / catching cold in summer / summer diarrhea / air-conditioning sickness / summer fever with chills / Huo Xiang Zheng Qi Wan / sleeping outdoors and getting chilled / gastrointestinal-type cold

Medical terms for this condition: yin shu (summer-heat cold-damp) · cold-damp trapping the spleen · externally contracted wind-cold · gastrointestinal-type cold

Opening: even African exchange students want to “go back to Africa to escape the heat”?

This year’s summer heat — you have all felt it. Even the northeast climbed to thirty-four or thirty-five degrees. Friends actually traveled from the south to the north to escape the heat, arrived, and found the north was hotter than the south. People joke online: there were African exchange students who got heatstroke here and announced they were going back to Africa to cool off.

💬 Note from Doctor Luo: You see how hot our temperatures get. To dodge this brutal heat, people try every way to cool down — but what you never expected is that when the way you cool off is wrong, it is precisely what makes the body break down. Chinese medicine has a name for this kind of problem: yin shu (summer-heat cold-damp).

What exactly is “summer-heat illness”? Modern medicine and the ancients disagree

To talk about yin shu, we have to start with “shu” — summer-heat. Of the six qi (wind, cold, summer-heat, dampness, dryness, fire), summer-heat is the one called shu wei re zhi ji — summer-heat is heat pushed to its extreme. The “heatstroke” we usually talk about is very clearly described in modern medicine:

💬 Note from Doctor Luo: Modern heatstroke happens because the outside environment is so hot that the body keeps losing fluid, and in the end the heat-dissipating function fails — you stop sweating, your temperature climbs, your pulse races, your skin turns hot and dry, your muscles go limp, and then come coma, collapse, even death. The critical treatment is just two things: cool the surroundings and replenish fluids. Handle it in time and the body recovers quickly.

But the ancients used “summer-heat illness” much more broadly — besides extreme heat injuring the fluids, catching damp-heat pathogens also counted as summer-heat illness: vomiting and diarrhea, dizziness, thirst, all went under that name. Within this big concept, the ancients distinguished two kinds: yang shu and yin shu.

💬 Note from Doctor Luo: Damp-heat causes yang shu — that is the kind we talked about before. But there is a strange situation: in the great heat, people like to run into big mansions and basements, drink cold things, fan themselves without stopping — the weather is hot, so the pores are all open, and suddenly a gust of cold arrives, and cold-damp slips right into the body, producing cold-damp symptoms. This too is an illness caught in hot weather, yet the body is clearly in a cold pattern — the ancients called it yin shu.

Doctor Zhang Jingyue’s warning: yin patterns are most easily mistaken for heat patterns

Not everyone agreed with the name “yin shu” — Doctor Li Dongyuan had his own system.

💬 Note from Doctor Luo: Doctor Li Dongyuan divided things up more “amusingly”: he called heat-caused illness zhong re (struck by heat) and cold-caused illness zhong shu (struck by summer-heat). But I do not think his division is scientific, and it is not worth adopting — that is why it never spread; only he talked that way. It was the Ming-dynasty physician Doctor Zhang Jingyue who explained it clearly — he said summer-heat illness divides into yin and yang, and yin patterns must be taken seriously: many people run into trouble precisely because they do not know how to handle the yin pattern.

Why can’t people handle it? Doctor Zhang Jingyue put his finger on the crux: because the illness came in hot weather, everyone assumes it is a heat pattern — there, right there, is the mistake. A clear cold pattern treated as a heat pattern — how could that not make things worse? So recognizing yin shu is lesson number one for surviving the summer.

Bad habit number one: sleeping outdoors

So which habits actually let cold-damp sneak in during summer? Doctor Luo counts them off for us.

💬 Note from Doctor Luo: First, sleeping outdoors. Some people sleep outside at night — when I was at university, the dorms had no air conditioning, so we loved to sleep on the rooftop, where the breeze kept us cool. But listen: in the first half of the night the heat feels comfortable; in the second half the air turns cold, and many people are sleeping in shorts with bare chests, so the abdomen gets chilled easily. The next day: vomiting and diarrhea, stomach pain — that is cold-damp doing its work. Last night while I was walking down the street I saw a delivery boy asleep in the open bed of his truck — that is also sleeping outdoors, and it is very easy to catch cold-damp. Do not be fooled by the hot weather; this is a real way to get chilled.

Bad habit number two: cooling off in cold, damp places

The second trap is hiding out in cold, damp spots.

💬 Note from Doctor Luo: In the great heat, many people like to hide in air-conditioned rooms with the cold wind blowing. But when you step outside, it is scorching — your pores open, you sweat, and the moment you come back into that cold room, cold-damp invades the body. Some people live by the water, where the dampness is heavy to begin with. Some love to play mahjong in air-raid shelters — those basements are cold and damp, and stay too long and you will develop wind-dampness. Falling asleep without noticing in these cold, damp places ends in catching cold.

Bad habit number three: greedy cold food

The third one is not keeping the mouth in check — eating cold things.

💬 Note from Doctor Luo: In summer people love cold drinks — ice water pouring down by the glassful, “crystal clear, icy cool” — that is guaranteed to chill you. And the famous northeastern snack cold noodles (leng mian) even come with ice cubes in the bowl. Outside you are sweating from the heat and all you want is something frozen — the instant it goes down it feels wonderful, but very soon the spleen and stomach get chilled, and the illness that follows is also yin shu. Also, sleeping with an air conditioner or electric fan blowing strong wind straight at you — plenty of people get sick exactly this way.

Why is summer so easy to catch it?

You might ask: cold-damp is cold-damp, so why does cold in summer hurt especially badly?

💬 Note from Doctor Luo: Normally the body keeps a certain guard against the environment — but in summer the body is at its most relaxed: the pores are wide open, the body is hot inside, and it simply does not prepare against cold. When you let yourself get chilled with the guard completely down, the cold pathogen enters especially easily and the illness strikes faster. So the name “yin shu” makes sense: the cold you catch in summer-heat weather — the cold-damp you take in — is easier to fall ill from, and it strikes more quickly. In plain words: in scorching hot weather, you got hurt by cold-damp.

What are the symptoms of yin shu? Check yourself

Once yin shu takes hold, the body sends out a string of signals — first the externally contracted signs, then the spleen-and-stomach signs.

💬 Note from Doctor Luo: People with yin shu tend to have an externally contracted picture: fever with chills — they do run a fever, but they fear the cold; little sweating, some have none at all, the skin all over feels tight, cold, goosebumpy, and dry to the touch; the body feels heavy, deeply achy, without strength; the whole person is stupefied, the head dizzy and heavy, the mind foggy, not an ounce of energy. Look at the tongue: the tongue body is pale — a red tongue body indicates heat; when you catch cold pathogen and your yang qi is insufficient, the tongue color turns pale; the coating is white (sometimes tinged yellow), often spread across the whole tongue, and greasy.

When the spleen and stomach are injured by cold, the symptoms are even more direct: abdominal pain, diarrhea, vomiting and diarrhea, total weakness, aching joints. That is yin shu.

How to treat it? Remember one sentence: this is a cold pattern — use hot medicines

Once yin shu strikes, the ancients long ago had ready-made treatments — it all depends on where the damage is.

💬 Note from Doctor Luo: If the externally contracted symptoms are obvious, treat it as wind-cold, for example with Zheng Chai Hu Yin (Rectifying Bupleurum Drink) — that is Doctor Zhang Jingyue’s formula for externally contracted wind-cold. Doctor Zhang Jingyue also said that if your upright qi is insufficient and your yuan qi (source qi) depleted, you can take Bu Zhong Yi Qi Wan (Tonify the Middle and Augment Qi Pill) or the decoction — once the upright qi is filled up, the cold pathogen disperses on its own; you do not necessarily have to attack the pathogen. If the spleen and stomach are injured by cold, use warming-yang medicines like Fu Zi Li Zhong Wan (Aconite-Stewed Regulate-the-Middle Pill) — everyone, remember: you must use hot medicines.

Is there something most on-point? Yes — Huo Xiang Zheng Qi Wan (Agastache Upright Qi Pill) and Huo Xiang Zheng Qi Shui (Agastache Upright Qi Liquid).

💬 Note from Doctor Luo: Everything inside Huo Xiang Zheng Qi is cold-damp-dispelling Chinese medicine, which is why people used to say “Huo Xiang Zheng Qi cures heatstroke” — but be very clear: it does NOT cure the heat-pattern heatstroke! If you truly caught heat, all those warming herbs in Huo Xiang Zheng Qi would be the wrong thing to take. What it cures is yin shu — when you have caught cold-damp, the spleen and stomach are injured, there is vomiting and diarrhea, a little nausea, fever — in that situation Huo Xiang Zheng Qi works especially well. That is the gastrointestinal-type cold, and Huo Xiang Zheng Qi fits it perfectly.

The biggest trap: grabbing cooling medicine whenever you have a fever

Finally Doctor Luo especially warns about the most common misunderstanding — clearing heat and toxins the moment you feel feverish.

💬 Note from Doctor Luo: Some people do not understand. They feel feverish and grab cooling, heat-clearing medicines — no effect at all, and you feel worse and worse: bloating, food not digesting, and in the end the yang qi is injured. At this point you need warming medicines — even Gui Zhi Tang (Cinnamon Twig Decoction) works well. Some practitioners specialize in Gui Zhi Tang, others are good with Fu Zi Li Zhong. When the gastrointestinal symptoms are obvious, use Huo Xiang Zheng Qi. The ancients said yang shu and yin shu are like ice and charcoal — one is ice, one is fire; you must get it straight.

💬 Note from Doctor Luo: The weather is extremely hot right now, yet we are even more easily hurt by cold and cold-damp pathogens, producing yin shu. The illness is called “shu” — summer-heat — but it really means catching cold-damp. First, we must prevent: do not let yourself take in cold-damp. Second, once the body has a problem, remember you must use warming medicines to drive the cold out, and only then will the body gradually return to health.

In this blazing weather, keep the two words “yin shu” in mind, and at least you will know how to protect yourself — dodge the cold-damp, and you can get through this summer comfortably.

What to take away

Yin shu is the summer trap nobody expects: the hotter the day, the more relaxed the body’s guard, and the easier cold-damp slips in — fever with chills, little sweating, goosebumpy cold skin, heavy achy body, dizzy head, pale tongue with a white greasy coating.
Four habits let cold-damp in: sleeping outdoors (rooftops, truck beds — the second half of the night turns cold), cooling off in cold damp places (air-conditioned rooms, riverbanks, damp basements), greedy cold food (iced drinks, cold noodles with ice), and air conditioners or fans blowing directly on you.
The number-one mistake is treating it as heat: because the illness comes in hot weather, everyone reaches for cooling, heat-clearing medicines — no effect, worse bloating, injured yang qi. This is a cold pattern; you must use warming medicines, even Gui Zhi Tang works.
Match the medicine to the injury: obvious wind-cold symptoms — Doctor Zhang Jingyue’s Zheng Chai Hu Yin (Rectifying Bupleurum Drink); deficient upright qi — Bu Zhong Yi Qi Wan (Tonify the Middle and Augment Qi Pill); spleen and stomach chilled — Fu Zi Li Zhong Wan (Aconite-Stewed Regulate-the-Middle Pill).
Huo Xiang Zheng Qi Wan/Shui is the most on-point medicine — but only for yin shu and gastrointestinal-type colds (cold-damp injuring the spleen, vomiting and diarrhea, nausea with fever); take it for a true heat heatstroke and all those warming herbs will make things worse.
Yang shu and yin shu are like ice and charcoal — tell them apart. Prevent cold-damp in the first place; if you are struck, drive the cold out with warm medicines.

Compiled from Doctor Luo Dalun’s health lecture (the content of the case histories and health guidance was narrated by Doctor Luo Dalun; the classical doctrines involved come from the Complete Works of Jingyue (Jing Yue Quan Shu) and other classics).