Roots and rhizomesHeat-clearingArnebiae Radix

Zi Cao (Redroot Gromwell)

A practical guide to Zi Cao: what it is, how Traditional Chinese Medicine uses it, the classical formulas it appears in, and who should be careful with it.

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Last reviewed Oct 29, 2026

Quick Facts

Latin Name	Arnebiae Radix
Chinese Name & Pinyin	紫草 · Zi Cao
Medicinal Part	Roots and rhizomes
The item	Zi Cao is the dried root of gromwell, used raw or wine-processed. It usually goes into decoctions, and external use goes into ointments.
Nature and channels	Bitter, cold. Enters the Heart and Liver. It clears heat from the blood, promotes rash eruption, resolves toxin, and fades macules.
Pharmacopoeia line	Clears the blood and promotes rash eruption. Resolves toxin and fades macules. Used for incompletely erupting rashes, dark purple macules from warm disease, and red swollen skin sores.
Pattern cues	Incompletely erupting rash. Dull rash color with fever. Dark purple macules. Red swollen skin sores.
In this article	Zi Cao versus Chi Shao. Clearing the blood versus breaking up stasis. Why the dose stays small. Why pregnancy is a caution. Why feverish rash needs a clinic. Who should skip it.

What Is Zi Cao?

Zi Cao (紫草; Zǐ Cǎo; Latin: Lithospermum erythrorhizon; English: gromwell root) in the current pharmacopoeia is the dried root of a borage-family perennial, dug in spring or autumn and used raw or wine stir-fried. It is bitter and cold, enters the Heart and Liver channels, and its core actions are to clear heat from the blood and promote rash eruption, and to resolve toxin and fade macules. It usually goes into decoctions. The usual amount is 3–10 g. It needs no special cooking order. External use is often made into an ointment applied to the affected skin.

It is not Chi Shao. Red peony root is bitter and cold too, but it cools the blood and breaks up stasis; it does not promote rash eruption. Spleen-stomach deficiency cold with frequent abdominal pain and diarrhea is a poor match. Use caution in pregnancy and lactation. A rash that has fully surfaced with no heat-toxin should not be topped up. Allergy to borage-family plants is a hard skip. Red swollen skin sores with pus need pattern diagnosis.

It is used most often for three patterns:

Incompletely erupting rash with fever and restlessness — seek care
Dark purple macules in warm disease — seek care
Red swollen skin sores and eczema

Bitter and cold, it is not a daily “rash tea” to keep increasing. Clearing and surfacing when there is no heat-toxin chills the spleen and consumes the upright qi.

When warm-toxin enters the blood level and the rash-toxin cannot surface, the rash emerges incompletely with a dull color, and dark purple macules appear with fever and a crimson tongue. Zi Cao is bitter and cold. It clears heat from the blood, promotes eruption, and resolves toxin, which is why it appears in Zi Cao Xiao Du Yin (Gromwell Detox Drink)–type formulas. It disperses more than it holds. A cold weak spleen and stomach, with no heat, get worse if more is added.

Zi Cao is not a catch-all rash or skin herb. In spleen-stomach deficiency cold, with no heat-toxin, or in pregnancy and lactation, using it alone is a poor match. Raw or wine-processed, and whether it belongs in a formula, should be decided by a licensed Chinese medicine practitioner after pattern diagnosis.

Zi Cao: Materia Medica Profile

Identification & Quality Standard

Arnebiae Radix

Botanical Origin

The dried root of Lithospermum erythrorhizon Sieb. et Zucc.(ying zi cao), Arnebia euchroma (Royle) Johnst(ruan zi cao), Arnebia guttata Bge.. (Boraginaceae)

Production Regions

Primarily produced in the Chinese provinces of northeast and Inner Mongolia.

Quality Requirements

Superior medicinal material has thick strips, thick cortex, purple color.

Macroscopic Features

Ying zi cao: Conical, curved, with branches, 7~14cm long, 1~2cm diameter. Externally purplish-red or purplish-black, rough with longitudinal wrinkles, thin cortex, easily falls off. Hard and brittle texture, easily broken, fractured surface has dark purple cortex, relatively large xylem, and grayish-yellow. Distinctive aromatic odor, sour and sweet taste. Ruan zi cao: irregular long cylindrical, often curved, 7~20cm long, 1~2.5cm diameter. Externally purplish-red or purplish-brown, loose cortex, which is flake-like, often has about 10 layers overlapped, easily falls off. Branched remnants of stem can be seen at the apex. Soft texture, loose, easily broken, fractured surface is coarse, relatively small xylem, yellow or yellowish-white. Distinctively aromatic odor, bitter and astringent taste. Arnebia guttata Bge.: slightly thin cortex, often numerous layered, easily falls off, hard and brittle texture, relatively neat fractured surface, relatively small xylem.

Main Regions and Quality Identification

Traditional materia medica and industry experience value the Inner Mongolia and Xinjiang producing regions, though actual quality also depends on variety, harvest time, processing, and storage. In appearance, good-quality Zi Cao root is conical, with a dark purple-red surface and twisted longitudinal grooves; the texture is hard and brittle; the cross-section shows a purple-red bark zone with a small wood zone, a faint odor, and a slightly bitter taste. The common look-alikes are roots of other plant families — such as certain red-root weeds — which lack Zi Cao's characteristic purple-red bark zone and have a fainter odor; they are easy to tell apart by appearance and smell.

Traditional Properties & Historical Lineage

Nature, Flavour & Channel Tropism

Sweet, Salty; ColdHeartLiver

1. Records in Classic Materia Medica

Shen Nong Ben Cao Jing: records — "Zi Cao treats evil qi of the heart and abdomen, the five kinds of jaundice, tonifies the middle and boosts the qi, benefits the nine orifices, and frees the water passage."
Ming Yi Bie Lu: adds — "Zi Cao treats abdominal swelling, fullness, and pain; mixed into a paste, it treats children's sores and facial acne."
Xin Xiu Ben Cao: notes it "treats swelling, fullness, and pain; mixed into a paste, it treats children's sores and facial acne."
Ben Cao Gang Mu: says it "treats macules, rash, and pox; constipation; dissolves accumulated toxin; treats evil qi of the heart and abdomen; and frees the water passage."

These records all circle around its clearing-freeing and rash-promoting actions, without exaggeration.

2. How Views of Its Nature Changed

Different physicians saw it somewhat differently. The early Shen Nong Ben Cao Jing mentioned a "tonifying the middle and boosting the qi" action, but many later physicians held that Zi Cao is a bitter-cold herb, leaning toward clearing and draining, without a tonifying effect — better suited to patterns with heat or rashes failing to erupt, and not suited to people with spleen-stomach cold and frequent diarrhea. Some physicians stressed its penetrating-dispersing side, holding that it helps the rash-toxin surface; others warned of its cold nature — that overuse harms the spleen-stomach yang.

Core Efficacies & Traditional Applications

Traditional Functions

Clears heat and cools blood, activates blood, and resolves toxin and erupts rashes.

1. First Direction: Clearing and Freeing the Blood, Promoting Rash Eruption

Traditional action: clear the heat evil of the blood level and promote the eruption of rash-toxin — letting the rash-toxin surface through the body's exterior while clearing the heat evil in the blood.
Typical signs: mainly used after febrile illness when the rash fails to erupt smoothly or emerges incompletely — a dull rash color with fever, restlessness, and thirst (blood-heat patterns) — and also for red, swollen skin when the rash has emerged but the heat-toxin is not fully spent.
Usual combinations: clinically often paired with Chan Tui and Niu Bang Zi to strengthen the eruption; with marked blood-heat, with Chi Shao and Mu Dan Pi to strengthen the clearing of blood heat.
Who should not self-use: those with spleen-stomach cold and frequent abdominal pain and diarrhea, or those whose rash has fully erupted without heat-toxin signs — self-use may worsen the deficiency-cold symptoms.

2. Second Direction: Resolving Toxin and Fading Macules

Traditional action: clear the heat-toxin in the blood and help fade the skin macules — especially the dark purple macules of heat entering the blood level.
Typical signs: mainly for febrile skin macules — dark purple color with fever, restlessness, and a red, crimson tongue (blood heat-toxin patterns) — and also for early skin sores with redness, swelling, and pain.
Usual combinations: often paired with Da Qing Ye and Ban Lan Gen to strengthen toxin-resolving and macule-fading; with darker macules, with Tao Ren and Hong Hua to help activate the blood and fade the macules.
Who should not self-use: those with pale macules and deficiency-cold signs — fear of cold, cold hands and feet — to avoid harming the yang.

3. Classic Pairing: Zi Cao With Chan Tui

The classic herb pair is Zi Cao with Chan Tui. Chan Tui disperses wind-heat, promotes eruption, and stops itching; Zi Cao clears the heat evil of the blood level, promotes eruption, and resolves toxin. Together they both disperse the wind-heat at the body's exterior and clear the heat-toxin in the blood — strengthening the eruption-promoting and toxin-resolving effect — suiting the febrile patterns of rashes that fail to erupt smoothly, a dull rash color, and skin itching. This pairing needs a practitioner's pattern diagnosis; don't combine herbs on your own.

Modern Research

Modern research offers useful context, but Traditional Chinese Medicine prescribes on whole-pattern diagnosis rather than isolated compounds.

1. Main Chemical Constituents

Detected constituents are mainly naphthoquinones — including shikonin, acetylshikonin, and isobutyrylshikonin — plus some polysaccharides and flavonoids. In vitro experiments observed that the naphthoquinone constituents can inhibit the growth of some bacteria and fungi to a certain degree; animal experiments observed that the extract helps reduce skin inflammation in mice. No sufficient human clinical study has yet reached a clear efficacy conclusion.

2. Current Research Directions

Current pharmacological research focuses on several directions: the regulation of skin inflammation, the potential effect on immune function, and observations related to pigment metabolism. In skin inflammation models, some components helped lower the levels of inflammatory factors — but more human studies are still needed to verify whether these effects translate into actual clinical results.

3. Limitations of Current Research

Lab results are not clinical efficacy — in vitro and animal results cannot be directly equated with the same effect after a person takes Zi Cao, because the human physiological environment differs greatly from the experimental environment.
Extracts and monomers are not the same as traditional decoction pieces — the Zi Cao extracts or single components used in modern research differ from the daily-use slices in extraction method and active-component content; they cannot be converted directly.
Doses and preparation methods vary between studies — differing doses and extraction methods across studies may bring inconsistent results, so the actual effect cannot be uniformly stated.
A single component does not define the whole herb — Zi Cao's action is the result of many components working together; detecting one component with a specific action does not mean the whole herb's effect is just that.

Comparing Similar Herbs

1. What They Share

Zi Cao and Chi Shao are similarly acting herbs often mentioned together. They share three main points:

Both have clearing the heat evil of the blood level as a main action — helping ease the discomfort that blood-heat brings.
Both are used for blood-heat patterns of febrile illness — such as skin macules and a red, crimson tongue.
Both need constitution and dose care — people with cold constitutions should use both with caution and avoid excess.

2. The Key Differences: Zi Cao vs. Chi Shao

Nature and flavors: Zi Cao is cold with a bitter flavor, leaning toward penetrating-dispersing — helping the rash-toxin surface; Chi Shao is also cold with a bitter flavor, but leans toward cooling the blood and activating the blood — clearing the heat evil of the blood level while activating the blood, without an obvious penetrating-dispersing quality.
Focus: Zi Cao excels at promoting rash eruption and resolving toxin — mainly for rashes failing to erupt or rash-toxin sinking inward, and it also resolves toxin and fades macules for skin macules; Chi Shao excels at cooling the blood and activating the blood — mainly for blood-heat macules, vomiting blood, nosebleed, and stasis-blocked pain, focusing more on activating blood and dissipating stasis.
Qi tendency: Zi Cao leans toward scattering — letting the pathogen surface through the body's exterior without lingering inside, a "scattering" action; Chi Shao leans toward clearing-draining and activating — clearing the heat evil of the blood while driving the blood to move, a "draining" and "freeing" action.
Best fit: Zi Cao's traditional indications are rashes failing to erupt, a dull rash color, or macules with incomplete eruption; Chi Shao's indications are red macules, bleeding from blood-heat rash, or pain from stasis.
Not suitable: Zi Cao is not for spleen-stomach cold with frequent diarrhea, nor for those whose rash has fully erupted without heat-toxin; Chi Shao is not for spleen-stomach cold with frequent abdominal pain and diarrhea, nor for blood deficiency without heat and without stasis.
Use scenes: Zi Cao appears in formulas for febrile rashes failing to erupt — such as pediatric measles formulas — and in external ointments for skin sores; Chi Shao appears in formulas for blood-heat bleeding and stasis pain — such as vomiting blood and fall injury, and gynecologic dysmenorrhea formulas for stasis blockage.

3. One-Sentence Summary

Simply put, Zi Cao leans toward promoting rash eruption and resolving toxin — for rashes that fail to erupt, whereas Chi Shao leans toward cooling the blood and activating the blood — for blood-heat bleeding and stasis pain. Both can be used for blood-heat macules, but they are not interchangeable.

Classical Formulas Containing Zi Cao

Classic Formula 1: Zi Cao Xiao Du Yin (Gromwell Detox Drink)

Combination logic: In the lord-minister-assistant-emissary structure of Zi Cao Xiao Du Yin, Zi Cao is the lord — at the core, mainly addressing rashes failing to erupt and heat-toxin internally flourishing. With Chan Tui and Niu Bang Zi it strengthens the eruption; with Jin Yin Hua and Lian Qiao it strengthens the toxin-resolving; with Huang Lian and Zhi Zi it strengthens the clearing of blood heat-toxin. It is not used alone: a rash failing to erupt usually comes with wind-heat and heat-toxin, and several herbs working together are needed to cover the eruption-promoting, toxin-resolving, and heat-clearing needs at once — Zi Cao alone is too single in action to cover all the pattern needs.

Traditional use: traditionally for pediatric measles with rashes failing to erupt — a dark purple rash with fever, restlessness, thirst, and a sore swollen throat — the pattern of rash-toxin internally flourishing — helping the rash-toxin surface and clearing the heat-toxin, to avoid the bad outcomes of rash-toxin sinking inward.

Modern note: modern clinical use requires a doctor's pattern diagnosis and standard care; do not self-apply just because the formula name relates to pediatric measles. Modern disease presentations may differ from the traditional patterns, so the herbs need adjustment to the specific situation to stay safe and effective.

Classic Formula 2: Zi Cao Gao (Gromwell Ointment)

Combination logic: In Zi Cao Gao, Zi Cao is the lord — the core herb for resolving toxin, fading macules, moistening the skin, and generating flesh — mainly addressing skin sores and red swollen macules. With Dang Gui and Bai Zhi it activates the blood, reduces swelling, generates flesh, and stops pain; with Qing Fen and Xue Jie it strengthens the toxin-resolving and sore-healing effect. Zi Cao alone cannot cover both the blood-activating and sore-healing needs — other herbs working together are needed for a better external effect.

Traditional use: traditionally for pediatric skin sores, eczema, red swollen macules, and ulcers that fail to heal — applied externally to resolve toxin, fade macules, moisten the skin, and generate flesh, promoting skin recovery.

Modern note: modern clinical use requires a doctor's pattern diagnosis and standard care; do not self-use even though it is an external ointment. Skin problems come in many types and need different handling; self-use may worsen the skin damage.

Formulas vs. Single Herbs

A formula is a whole worked out by many herbs together — every herb's dose and combination are carefully designed, covering multiple sides of the pattern, and the herbs synergize and check each other. A single herb cannot simply replicate a full formula's effect, because it lacks the synergy and checks of other herbs — its action is more single and cannot cover complex pattern needs. The common misunderstanding to point out: that because a herb works inside a formula, taking it alone works the same way — in fact, the formula's effect is the result of many herbs working together, not a simple addition of single herbs.

Diet & Daily Home Use

1. Home Tea

Tea — Zi Cao Yin Hua Cha: Zi Cao 3 g, Jin Yin Hua 2 g, Ju Hua 2 g. Put all the ingredients in a cup, steep in boiling water for 10 minutes, and drink; can be re-steeped until the taste fades. Suited to the early stage of a febrile illness — mild skin itching, dry mouth, and throat discomfort — or mild pediatric red skin rash with restlessness. Not for those with spleen-stomach cold and frequent abdominal pain and diarrhea, nor pregnant women, breastfeeding women, children, or people allergic to related plants. Suggested: no more than 2 times a week, no more than 1 cup each time; not for long-term continuous drinking. Reminder: Zi Cao is a medicinal decoction piece — don't treat it as an ordinary food and use it freely; it is best to consult a doctor or pharmacist before drinking.

2. Decoction and Processing Differences

The difference between raw and wine-processed Zi Cao is mainly in processing method and use: the raw product leans toward clearing the heat-toxin of the blood level, better for internal decoction to treat heat patterns; Jiu Zi Cao, after wine stir-frying, has a somewhat reduced cold nature, better for promoting eruption, and its active components extract more easily. At home, put Zi Cao in a sand pot with water, soak for 30 minutes, bring to a boil on high heat, then simmer for 20 minutes on low heat, filter, and take the liquid. Zi Cao needs no special decocting method — no pre-boiling or late addition; ordinary home decocting works. Different forms cannot be converted directly: for example, 10 g of Zi Cao slices is not the same as 1 g of Zi Cao extract, because the active-component content and extraction method differ.

3. Dosage and Course

The common dose range in traditional prescriptions is 3–10 g, adjusted by pattern and constitution. Food-therapy doses are smaller than medicinal ones — generally no more than 5 g, for daily mild regulation. Long-term continuous use is not advised: continuous use is best kept under 1 week, to avoid harming the spleen-stomach yang. Special groups — children, the elderly, pregnant women, and people with liver or kidney impairment — must consult a doctor or pharmacist before use; do not decide the dose and duration on your own.

Contraindications & Safety Warnings

1. Who Should Avoid It

Spleen-stomach cold with frequent abdominal pain and diarrhea — Zi Cao's cold nature may worsen the spleen-stomach deficiency-cold symptoms.
Pregnancy and breastfeeding — use with caution; there is not enough research proving its safety.
Children and the elderly — weaker tolerance; do not self-use, use under a doctor's guidance.
Liver or kidney impairment — avoid use, to avoid adding burden to the liver and kidney.
Allergy to Zi Cao or Boraginaceae (borage-family) plants — strictly forbidden.
Those in special treatment — such as anticoagulants, blood-pressure medications, blood-sugar medications, or sedatives — consult a doctor before use, to avoid interactions.

2. Interactions and Diet Notes

Zi Cao may interact with anticoagulants, affecting coagulation function — those taking anticoagulants should use it with caution; it may also interact with some blood-pressure and blood-sugar medications, affecting drug absorption or metabolism — those taking these should consult a doctor. There is no sufficient evidence for a general "food clash" between ordinary foods, but certain herbs can interact with specific drugs — anyone on medication should consult a doctor or pharmacist first and not combine herbs on their own.

3. Adverse Reactions and Overdose Risk

Overuse may worsen spleen-stomach cold — abdominal pain, diarrhea, nausea, and vomiting — and may also cause dizziness and fatigue. If marked discomfort or allergy signs appear — such as red swollen skin, itching, breathing difficulty — or persistent vomiting, altered consciousness, or rapidly worsening symptoms, stop at once and seek medical care — don't delay.

Frequently Asked Questions About Zi Cao

What is Zi Cao? Are Zi Hua Di Ding and Jin Yin Hua the same?

Zi Cao (紫草) is the dried root of Arnebia euchroma or Lithospermum erythrorhizon (Arnebiae Radix), a common Chinese herb centered on cooling the blood and invigorating blood, detoxifying and venting rashes. Zi Hua Di Ding clears heat and detoxifies, leaning to sores. Jin Yin Hua clears heat and detoxifies, leaning to wind-heat. The three cannot be interchanged by equal weight. Write Zi Cao. Use caution in Spleen deficiency with loose stool.

What is the composition and traditional use of Zi Cao?

Pharmacopoeial name Zi Cao, Latin Arnebia euchroma or Lithospermum erythrorhizon. Sweet and salty, cold; enters the Heart and Liver channels. It acts to cool the blood and invigorate blood, detoxify and vent rashes. It is used for heat-toxin exuberance in the blood, purple-black macules and rashes, measles that fail to vent, sores, eczema, and burns. Cools the blood, detoxifies and vents rashes.

How do you choose raw versus prepared? Can Zi Hua Di Ding replace it?

Sliced and used raw or prepared as an ointment for external use. Zi Hua Di Ding leans to detoxifying without specialized rash-venting; it cannot replace the formula by equal weight. Commercial products follow regulated processing; do not self-modify.

What is the usual dosage? Can it be drunk daily as a blood-cooling tea?

Decocted, 5-10 g. Modern use requires a practitioner to name the dose. It is not a four-season “arnebia tea.” Spleen deficiency with loose stool only injures further. Macules and rashes need a practitioner to name a short course; it does not replace assessment.

What are the contraindications? Can it be used in pregnancy?

Contraindicated in Spleen deficiency with loose stool. Pregnancy requires practitioner assessment. Stop if loose stool or abdominal pain appears. Worsening macules or high fever need immediate medical care.

Can Zi Cao cool the blood and invigorate blood, detoxify and vent rashes?

It can help heat-toxin exuberance in the blood with purple-black macules, measles that fail to vent, sores, eczema and burns. It cools the blood and invigorates blood, detoxifies and vents rashes—not a specific for every macule or every sore.

Can Zi Cao be drunk daily as a blood-cooling or detoxifying tea?

Blood-heat macules may enter a short formula; Spleen deficiency with loose stool only injures further. “Arnebia must vent rashes” does not replace assessment. Cooling the blood and invigorating blood, detoxifying and venting rashes should be named by a practitioner with form and dose.

How do you choose among Zi Cao, Zi Hua Di Ding, Jin Yin Hua, Lian Qiao and Sheng Di Huang?

Zi Cao cools the blood and invigorates blood while detoxifying and venting rashes, leaning to blood-heat macules. Zi Hua Di Ding clears heat and detoxifies, leaning to sores. Jin Yin Hua clears heat and detoxifies, leaning to wind-heat. Lian Qiao clears heat and detoxifies while dissipating nodules, leaning to abscesses. Sheng Di Huang clears heat and cools the blood, leaning to heat entering the ying and blood. Blood-heat macules favor Zi Cao; sores favor Zi Hua Di Ding; wind-heat favors Jin Yin Hua; abscesses favor Lian Qiao; ying-blood favors Sheng Di Huang. They may be referenced after pattern differentiation; Spleen deficiency with loose stool forbids large Zi Cao.

How is Zi Cao commonly modified? What is the representative use?

Depends on the pattern. Macules may add Lian Qiao; eczema may be used externally. Write Zi Cao; do not replace the rash-venting action with an equal weight of Zi Hua Di Ding.

How do you choose and store Zi Cao?

Choose regulated Chinese medicinal materials with intact roots. Moldy, damp, or abnormal-smelling lots are discarded. Store cool and dry. Buy “Zi Cao”; do not replace cooling the blood and invigorating blood, detoxifying and venting rashes with an equal weight of Zi Hua Di Ding or Jin Yin Hua.

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Medical Disclaimer — This article is provided for educational purposes only and describes traditional Chinese medicine concepts. It is not medical advice, and it is not intended to diagnose, treat, cure or prevent any disease. Always consult a qualified practitioner before using any herb, particularly if you are pregnant, nursing, taking medication or managing a diagnosed condition.