If you have browsed the ingredient lists on our products, you may have noticed a name that appears again and again: Arnebia euchroma, also called Arnebia root or Redroot. This is the botanical name for Zi Cao (紫草), one of the most important and most researched herbs in Traditional Chinese Medicine dermatology. Understanding what it is and why it keeps showing up may change the way you think about herbal skincare.
What Is Zi Cao?
Zi Cao is the dried root of plants from the Arnebia and Lithospermum genera, members of the Boraginaceae family. The name translates as "purple herb," a reference to the root's striking purple-red color, which comes from its primary active compounds, shikonin and its derivatives. These pigments are responsible both for the herb's characteristic color and for many of its most studied properties.
Zi Cao was first recorded in the Shennong Bencao Jing (Shennong's Classic of Materia Medica), a foundational Chinese herbal text compiled during the Eastern Han Dynasty, approximately the first to second centuries CE. While the original text of this book is no longer intact, the reconstructed versions record Zi Cao as being used to "clear heat and resolve toxin," a Traditional Chinese Medicine action that is similar (but not equivalent) to modern day anti-inflammatory actions. Resolving toxin also refers to the possibility of some kind of pathogen present, such as a bacteria, virus or fungus. It was also noted to be used as a topical application to promote blood circulation in wounds and for skin eruptions and inflammatory conditions.
The Bencao Gangmu (Compendium of Materia Medica), the later and much larger herbal text compiled by Li Shizhen and published in 1596 CE during the Ming Dynasty, expanded on Zi Cao's known therapeutic actions. The Bencao Gangmu came roughly 1,400 years after the Shennong Bencao Jing! As you can see, there is a long history of Zi Cao's use for it's healing qualities.
How TCM Understands Zi Cao
In Traditional Chinese Medicine (TCM), every herb has a set of properties that describe how it acts in the body. Zi Cao is considered a cold herb, meaning it is used when the body or skin has too much heat. It enters the Heart and Liver meridians, which in TCM terms means it has a particular ability to help blood flow and to clear heat that is deep in the body at the level of the blood, as opposed to simply sitting on the surface of the skin.
In plain terms, here is what TCM practitioners have historically used Zi Cao for:
Cooling blood that is too hot. In TCM, when the blood is overheated, it can push heat outward to the skin, causing red, inflamed, intensely itchy rashes. Zi Cao is one of the herbs TCM has long turned to for this kind of presentation.
Clearing heat and resolving toxin from the skin. This includes hot, swollen, painful, or infected-looking skin: what TCM might call Toxic Heat. Historically this included conditions like carbuncles (deep, painful skin infections), burns, measles rashes, and skin eruptions that looked infected or severely inflamed.
Topical wound support. For centuries, Zi Cao has been applied externally to burns, skin ulcers, wounds, and inflamed areas. This is one of the reasons it appears so consistently in topical products more often than it shows up in internal herbal formulations.
What makes Zi Cao particularly relevant to modern TCM dermatology is its specific affinity for skin conditions that involve heat in the blood: redness, inflammation, and the kinds of itching that are worse with heat exposure or at night. If you have read our article on understanding eczema through a TCM lens, you will recognize these as the Damp-Heat, Blood Heat, and Toxic Heat patterns. Zi Cao is one of the classical herbs for all three.
We do not recommend that people try this herb for any kind of condition or symptom without consulting with a certified TCM herbalist.
What Science Has Found
Zi Cao has attracted significant research interest in recent decades, particularly around its primary active compound, shikonin. The body of published research is now substantial enough to make some general observations. However, research into herbal compounds is ongoing and the science continues to develop.
Shikonin is known to exert anti-proliferative, anti-inflammatory, and antioxidant activities, and has been studied for its role in wound healing and skin repair. In recent decades, shikonin has been incorporated into topical preparations for study in a range of skin conditions. Properties that have been investigated in published research include anti-inflammatory, antioxidant, antibacterial, and wound-healing activities.
A meta-analysis published in a peer-reviewed journal examined Zi Cao and its active components specifically in relation to atopic dermatitis. A clinical trial found that an ointment containing shikonin significantly improved dermatitis scores in patients with atopic dermatitis. The same research team, using human dendritic cells derived from atopic dermatitis patients, showed that shikonin suppressed the expression of multiple allergen-induced pro-inflammatory cytokines and chemokines.
We encourage you to verify any specific research findings through resources like PubMed or OpenEvidence if you are investigating this topic in depth. The studies referenced here reflect published research as of mid-2026 and are not intended as medical claims about our products.
Why Zi Cao Appears in So Many of Our Formulas
When you understand what Zi Cao does in TCM terms, its prevalence in topical dermatology formulas makes complete sense. An herb that cools blood heat, resolves toxin, and has been used topically for inflammatory skin conditions for centuries is going to be a foundational ingredient for a formulary specializing in exactly those conditions. If you are not sure what patterns like Blood Heat or Damp-Heat mean for your skin, our eczema patterns article explains each one in plain language and helps you identify which might apply to you.
The products in our shop that contain Zi Cao (listed on the ingredient label as Arnebia Euchroma (Redroot) Root Extract) include some of our most-used formulas:
- Nourishing Cream (Zi Cao Shui Gao): The name itself references Zi Cao; our best-selling daily moisturizer suited to all eczema patterns
- Nourishing Ointment (Run Ji Gao): A richer ointment format of a similar formula to the Nourishing Cream, particularly suited to Blood Heat, Blood Dryness and Deficiency, and Wind patterns
- Soothing Cream (Shi Zhen Shui Gao): Suited to Blood Heat, Blood Dryness and Deficiency, and Wind patterns
- Nourishing Hand & Foot Cream (Run Zu Shui Gao): For dry, thickened, or cracked skin on the hands and feet
- Soothing Fingertip Ointment (Bai Ji Gao): For very dry, cracked, or sensitive fingertip skin
The fact that a single herb appears across this many formulas is not a coincidence. It reflects the centrality of blood heat and heat toxin patterns in inflammatory skin conditions, and Zi Cao's classical role in addressing exactly those patterns from the outside in.
Why the Purple Color Matters
If you have used Run Ji Gao (Nourishing Ointment) you will have noticed it has a distinctive deep red-purple hue. This is not artificial coloring. It is the shikonin in the Zi Cao. The depth of color in a Zi Cao-containing formula is often an indicator of the herb's concentration. This is also why some of our Zi Cao-containing products may leave a faint tint on fabric or light-colored surfaces before fully absorbing; always allow products to absorb fully before contact with fabric.
A Note on TCM Herbal Product Selection
Knowing that Zi Cao is in a formula does not automatically mean that formula is right for your skin. TCM dermatology involves matching the whole formula to the whole pattern, not just identifying one active ingredient. Two products that both contain Zi Cao may be suited to very different presentations depending on what other herbs they are combined with and in what proportions.
This is why we include TCM pattern information on many product pages, and why we encourage those with complex or longstanding skin concerns to seek an in-person consultation rather than self-selecting based on an ingredient list alone. Still, it is fun to learn about the power of our medicinal allies in nature. If you are looking for a qualified TCM dermatology practitioner, the International Traditional Chinese Medicine Dermatology Association maintains a practitioner directory at tcmdermatology.org.
If you are in Aurora or Denver, Colorado, Molly Dyer, L.Ac. offers consultations at Light & Dark Acupuncture & Apothecary.
The Herbal Skin Shop is an online apothecary curated by Molly Dyer, L.Ac., Board-Certified Clinical Herbalist and licensed acupuncturist. Products are selected for educational and general wellness purposes and are not intended to diagnose, treat, cure, or prevent any disease. Research references are provided for educational context only.
