What does a yellow tongue coating mean?

The tradition reads colour on the tongue the way a cook reads a pan. The coat is the stomach’s steam, and a healthy one is thin and white. Yellow is the colour of heat, and the deeper the yellow, the more heat: pale yellow is heat that has only just arrived, a deep or brownish yellow is heat that has settled in. So the first thing a yellow coat says is warm, and everything else about it says where the warmth is and what it has done.

Thin or thick is how far in the heat has got. Greasy is whether damp has come with it, and a yellow, greasy coat is the tradition’s damp-heat: a bitter or sticky mouth, heaviness with heat, dark urine. Wet or dry is whether the fluids are still intact, and a yellow coat that looks rough and dry is heat that has used them up. Before any of that, though, look again before breakfast. The coat is porous, and coffee, black tea, turmeric and tobacco colour it as easily as they colour a mug.

The yellow tongue is as old as the Neijing. In its chapter on needling heat, it is one of the signs of heat reaching the lung, listed with a shiver, a dislike of wind and a body that has grown hot.

The rule behind reading colour as temperature is among the Neijing’s nineteen lines on the workings of illness. Fluids that come out turbid belong to heat; fluids that come out clear and cold belong to cold. A coat is fluid made visible, and it is sorted the same way.

The Qing physicians made the yellow coat a gauge of heat against fluids. Ye Tianshi, whose talks his students wrote down in the eighteenth century, reads a yellow coat that is still slippery as heat that has not yet touched the fluids, and a thin one that has gone dry as heat that has left and taken the fluids with it.

Five pictures, one of them not a picture at all. The tongue under the coat decides most of it.

• Look before breakfast, in daylight, before coffee or tea. A yellow that has gone on a morning without coffee was the coffee.
• Less of what the tradition calls heating: alcohol, deep-fried and roasted food, very hot spice, lamb, and a great deal of red meat. Less sweet as well, since a greasy yellow coat is damp as much as it is heat.
• Cooling, not iced. Cucumber, pear, celery and green vegetables cool without chilling the stomach; iced drinks trade the heat for a cold, slow middle.
• Supper earlier and lighter. In the tradition’s account, a large meal eaten late sits in the stomach overnight and turns to heat.
• Sleep before midnight. In the tradition’s account, late nights spend the fluids that keep heat in check, and a dry coat is the sign they are running low.
• Enough to drink through the day, warm or at room temperature, sipped rather than gulped.

None of that is a promise, and we make none. A thin yellow coat from a cold usually clears with the cold; a thick one built over months takes months.

• Mulberry leaf 桑叶 with chrysanthemum 菊花, steeped together for five minutes, for the thin yellow coat and a sore, dry throat: the tradition’s pair for heat in the upper body.
• Job’s tears 薏苡仁, boiled with red beans, for the yellow, greasy coat: cool and bland, it lightens damp-heat.
• Mung beans, 绿豆, as a thin soup in hot weather, for heat of any kind.
• Pear, 梨, raw or stewed soft, for the yellow, dry coat and a dry throat.
• Ginger, cinnamon and ginseng are warm or hot, and are left out while the coat is yellow on a red tongue.

On the back of the hand, in the web between thumb and forefinger, is Hegu, Large Intestine 4, 合谷. The old rhyme gives it the face and the mouth, 面口合谷收, and it is the point classically paired with heat there: the sore throat and the thin yellow coat of a cold that has just begun. A firm squeeze, thirty seconds to a minute on each hand. It is avoided in pregnancy, and we mean that; if you are or might be, use Neiguan on the inner wrist instead. It is not a needle and it is not a claim about outcomes.