What is Zi Cao?

Zi Cao is the dried purple root of gromwell plants. The two plants used are Lithospermum erythrorhizon and Arnebia euchroma. In Chinese medicine it is used mostly on the skin.

It is put on red rashes, slow-healing sores, burns and nappy rash. It is also taken by mouth as a decoction (a strong tea). That use is for rashes said to come from "heat in the blood".

This is a single herb, not a ready-made formula. In traditional practice it is mixed with other herbs. The mix is matched to the person, not taken alone as a supplement.

Here is the honest evidence picture. Zi Cao has a long, well-recorded past in Chinese and Japanese herbal practice. But good human trials are very few.

Traditional use tells you what practitioners have long done. It is not proof that the herb works.

One safety point matters more than the rest. Some Arnebia and Lithospermum roots hold pyrrolizidine alkaloids. These are plant compounds that can harm the liver, so long or high-dose use by mouth is not safe.

How does Zi Cao work?

No one has shown in people how Zi Cao works. Treat any explanation as a theory, not a fact.

In traditional terms, Zi Cao is called cold and sweet-salty. It is said to "cool the blood" and clear heat and toxins. It is also said to move stuck blood and to loosen the bowels gently.

In lab tests, the purple pigments called shikonins slow the growth of some bacteria (germs). They calm swelling in cell and animal models. They also speed skin repair in animal wounds.

Lab results often do not carry over to people. None of these findings have been confirmed by solid human trials.

What forms does Zi Cao come in?

The most common form is an infused oil or ointment for the skin. The classic one is Zi Yun Gao, known in Japan as Shiunko. It is a purple salve of Zi Cao and Dang Gui in sesame oil and beeswax.

Other forms you may meet:

Dried root slices or root pieces, simmered with other herbs into a decoction (a strong tea).

Powdered root, stirred into ointment bases or dusted onto weeping skin.

Tinctures and liquid extracts, sold as single-herb products.

Everything it touches turns purple. That includes skin, nails, cloth and bedding. The stain fades but is hard to wash out, so use old sheets and clothes.

Where it comes from:

Zi Cao appears in the Shen Nong Ben Cao Jing. That is a Chinese herbal text from about the first to second century CE. It has been used ever since for rashes, measles-type eruptions and stubborn sores.

The purple ointment Zi Yun Gao was set down by the Japanese surgeon Hanaoka Seishu around 1800. It is still made today in Kampo (Japanese herbal medicine). That gives the herb a deep record in one linked family of traditions.

What does Zi Cao help with?

• Minor burns and scalds (skin care, once cooled): Traditional use is strong here; trial evidence is weak. Purple gromwell ointment is a standard household burn salve in China and Japan, applied after the burn has been cooled under running water. Small hospital studies exist, but we could not identify one we can cite with confidence. Never put oil or ointment on a fresh, hot burn, and never on a deep or blistered one.
• Nappy rash and skin irritation from moisture: A long-standing traditional use with only thin published testing in babies. The ointment forms a barrier and the herb is thought to calm redness. Because of the liver concern with these roots, do not give Zi Cao to a baby by mouth, and ask a doctor before using any herbal ointment on broken skin in an infant.
• Slow-healing sores and pressure sores: Used in hospitals in parts of East Asia as part of wound dressing routines, usually alongside standard care. Animal wound studies show faster skin closure, which is encouraging but not proof in people. Pressure sores need proper medical assessment; herbs are not a substitute for pressure relief and nursing care.
• Eczema and itchy inflamed patches: Traditionally used for hot, red, weeping skin rather than dry, scaly skin. Evidence in people is limited to case reports and small uncontrolled series. It will not replace prescribed creams, and the purple staining makes it awkward for visible areas.
• Haemorrhoids (swollen veins around the back passage): Zi Cao appears in several traditional ointments and suppositories for this. Published human testing is scarce and mostly in Chinese-language sources without clear controls. See a doctor about any bleeding from the back passage rather than treating it yourself.
• Measles-type rashes, in traditional internal use: Classical texts use Zi Cao in decoctions to help rashes come out and to cool the blood. This is a historical use recorded in a specific medical system, not a tested treatment. Measles and any widespread rash with fever need urgent medical care.

Which foods are rich in Zi Cao?

Zi Cao is a medicinal root, not a food. It is not eaten as part of any normal diet.

What are the side effects of Zi Cao?

• Deep purple staining of skin, nails, clothing and bedding
• Loose stools or diarrhoea, especially with internal use
• Nausea or stomach discomfort from decoctions
• Itching, redness or rash where the ointment is applied
• Allergic skin reaction (contact dermatitis)
• Liver injury with long or high-dose internal use, from pyrrolizidine alkaloids (liver-damaging plant compounds)

Good to know:

Staining is certain; the rest is uncommon. Skin reactions and loose stools are the usual complaints and settle when you stop.

The serious concern is the liver, and it comes from swallowing the root over time, not from ointment on intact skin. Signs of liver trouble include yellow skin or eyes, dark urine, itching all over and pain under the right ribs. Stop and get medical help if any of these appear.

How much Zi Cao should you take?

• Recommended daily: No safe or effective dose has been set by research. The numbers below come from traditional practice only. On the skin: a thin layer of purple gromwell ointment on the affected area, once to three times a day. By mouth: Chinese texts give 3 to 10 grams of dried root a day, simmered into a decoction and usually mixed with other herbs. Because of the possible pyrrolizidine alkaloids (liver-damaging plant compounds), internal use should only happen under a qualified practitioner who knows the species and source.
• Best time of day: No time of day works better than another. For skin use, many people apply it at night so the purple stain has time to absorb and does not mark daytime clothes. A decoction is usually split into two doses, morning and evening.
• With or without food: Skin use has nothing to do with meals. If you are taking a decoction, take it between meals as is traditional, or with food if it upsets your stomach. The herb loosens the bowels in some people, which is worse on an empty stomach.
• Time to effect: For minor skin irritation, people often report the area feels calmer within a few days. Wounds and sores change slowly and take weeks. If you see nothing at all after two weeks, stop and get it checked.
• How long to take it: Keep it short. For skin use, stop after about two weeks if nothing is improving and get the problem looked at. Internal use should be brief, measured in days to a couple of weeks, and not repeated as a long-term habit. Repeated or long courses raise the liver risk, which is the main reason to reassess early.