Herb reference

Mustard Seed

Sinapis alba L. (white/yellow mustard); Brassica juncea (L.) Czern. (brown/Indian mustard)

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Botanical / editorial

Family: Brassicaceae
Plant type: Annual herb
Route: Mixed route
Evidence tier: Mixed evidence

Mediterranean region, Central Asia5000+Brassicaceae

Botanical / meta

Botanical identity

Botanical description

Sinapis alba (white mustard) is an annual herb growing 30–100 cm tall with bright yellow four-petaled flowers and hairy stems, producing pale yellow seeds in slender, beaked pods (siliques). Brassica juncea (brown mustard) is similar but produces larger, lobed lower leaves and seeds that range from brown to black. Both species produce characteristic four-petaled cross-shaped (cruciform) flowers typical of the Brassicaceae family. The seeds are small, round, and hard, ranging in color from pale yellow to dark brown depending on species.

Pharmacognosy intro

Mustard seeds contain glucosinolates (mustard oil glycosides), principally sinalbin in white mustard (Sinapis alba) and sinigrin in brown mustard (Brassica juncea). When seeds are crushed and moistened, the enzyme myrosinase hydrolyzes these glucosinolates to produce volatile isothiocyanates (allyl isothiocyanate from sinigrin; p-hydroxybenzyl isothiocyanate from sinalbin) — these are the pungent, bioactive compounds responsible for mustard's characteristic heat and many of its pharmacological effects. Seeds also contain fixed oil (25–35%), proteins, and minerals.

Editorial orientation

The practical read

Body-first read

What it is for

Route panel

Preparation shapes the claim

Evidence and safety may differ by preparation. Essential oil, tea, tincture, extract, infused oil, and topical use are not interchangeable.

Mixed route

Quality

Fresh, dried, oil, and garden read

Growing tips

Easy to grow as a cool-season annual; sow seeds directly in early spring or autumn. Prefers well-drained, fertile soil in full sun. Fast-growing — harvest seed pods when they turn brown and begin to split. Mustard greens can be harvested as a leafy vegetable within 4–6 weeks. Self-seeds readily. Rotate crops — do not plant Brassica species in the same location year after year to prevent disease buildup.

Quality notes

White/yellow mustard seeds (Sinapis alba) are milder and used for prepared yellow mustard. Brown mustard seeds (Brassica juncea) are hotter and used in Indian cuisine, Dijon mustard, and Chinese hot mustard. Black mustard (Brassica nigra) seeds are the most pungent but are less commonly cultivated. Whole seeds store almost indefinitely; ground mustard loses pungency within months. To prepare hot mustard, mix ground seeds with cool water and let stand 10–15 minutes for maximum pungency (the myrosinase enzyme is destroyed by heat).

Companion

Crystal pairing reference

Crystal side

Companion crystal

The deeper layer

Compound and clinical layer

Clinical and compound notes are included as a research layer, not as treatment instructions.

Safety intro

HIGH RISK — Mustard plasters can cause severe skin blistering, chemical burns, and irritation if left on too long or applied to sensitive skin — never leave a mustard plaster on for more than 15 minutes. Do not apply to broken skin, face, neck, or genital area. Internal use of large quantities can cause gastric irritation, vomiting, and diarrhea. Contraindicated in pregnancy in medicinal amounts due to potential emmenagogue effects and uterine stimulation. Contraindicated in breastfeeding for internal medicinal use. Individuals with thyroid conditions should limit consumption of large quantities of raw Brassica seeds due to goitrogenic glucosinolate content. Allergic reactions to mustard are among the most common food allergies in Europe and can be severe. Culinary use in normal amounts is generally recognized as safe (GRAS).

Questions

Frequently asked about Mustard Seed

What are the critical safety warnings for mustard seed?

Mustard seed is high risk in its traditional plaster form: the allyl isothiocyanate released from crushed, moistened seed can cause severe skin blistering and chemical burns, so a mustard plaster should never be left on for more than 15 minutes and never applied to broken skin, the face, neck, or genital area. Taken internally in large quantities it can cause gastric irritation, vomiting, and diarrhea. In medicinal amounts it is contraindicated in pregnancy due to emmenagogue and uterine-stimulant potential and in breastfeeding for internal medicinal use. People with thyroid conditions should limit large quantities of raw Brassica seed because of goitrogenic glucosinolates. Mustard allergy is among the most common and potentially severe food allergies in Europe, though normal culinary use is GRAS.

How is mustard seed prepared and used medicinally?

Mustard's pungency and bioactivity only develop when the seeds are crushed and moistened, because that triggers the enzyme myrosinase to hydrolyze the glucosinolates (sinigrin in brown mustard, sinalbin in white) into volatile isothiocyanates. The classic preparation is a mustard plaster (poultice) of ground seed applied externally as a rubefacient for congestion and muscle pain, used briefly and watched closely to avoid burns. Hot water deactivates myrosinase, so cold or cool water is used when the goal is maximum pungency. Culinarily the ground seed is the basis of table mustard. The 15-minute external limit is the central safety rule.

How do you evaluate mustard seed quality and which type to use?

Quality mustard seed is firm, dry, and uniformly colored, with white/yellow seed (Sinapis alba) being milder and brown/Indian seed (Brassica juncea) being sharper because their glucosinolates differ: sinalbin yields the less volatile p-hydroxybenzyl isothiocyanate, while sinigrin yields the volatile, more pungent allyl isothiocyanate. Fresh, whole seed that releases a strong bite within a minute of being crushed and moistened indicates active myrosinase and intact glucosinolates. Pre-ground mustard loses pungency faster, since the volatile isothiocyanates dissipate once formed. Choosing white versus brown seed depends on whether mild or sharp heat is wanted.

What makes mustard seed's chemistry distinctive?

Mustard seed is distinctive because its activity is generated by an enzyme reaction rather than pre-formed in the seed: intact seed is nearly odorless, and only when crushing and moisture bring the enzyme myrosinase into contact with glucosinolates (sinigrin, sinalbin) are the pungent isothiocyanates produced. This myrosinase-glucosinolate system, shared across the Brassicaceae, is why preparation method dramatically changes potency and why hot water (which denatures myrosinase) blunts the heat. The resulting allyl isothiocyanate is both the source of mustard's culinary bite and its rubefacient and burn-causing power on skin. White and brown seed differ because they carry different glucosinolate precursors.

How should mustard seed be stored and what is its shelf life?

Whole mustard seed stores very well, keeping for 1-2 years or longer in an airtight container away from heat, light, and moisture, because the glucosinolates stay stable as long as the seed is dry and intact and myrosinase has not been activated. Moisture is the enemy, since any dampness can begin triggering the enzyme reaction prematurely and dull the seed. Ground mustard and prepared mustard lose pungency much faster, as the volatile isothiocyanates escape once formed, so grinding fresh is best for maximum heat. The fixed oil (25-35%) can eventually go rancid, so very old seed should be checked for off odors.

Sources & Citations

Where this entry can be checked

Peer-reviewed sources for the pharmacological and clinical claims on this page. Crystalis herb entries describe tradition and current research; they are reference, not medical advice.

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SCI
Exploring the bioaccessibility, in vitro colonic fermentation, and the impact on the intestinal microbiota of allyl- and benzyl-isothiocyanate
Cámara-Martos F, Iturbe-Atela A, Moreno-Rojas R. (2025). Exploring the bioaccessibility, in vitro colonic fermentation, and the impact on the intestinal microbiota of allyl- and benzyl-isothiocyanate. Food Research International. [SCI]DOI 10.1016/j.foodres.2025.115781

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