Single-oil monograph
Sweet fennel (Foeniculum vulgare var. dulce)
- Phototoxic No phototoxicity
- Pregnancy Avoid
- Pets Caution
Published 2026-10-20 · adult ceiling 2% · shelf life 24 months
Sweet fennel is 68% trans-anethole, which puts it in the same chemical group as anise and star anise and gives it the same avoid rows. It is the oil most often recommended for digestion and for menopause, and both of those recommendations are oral traditions applied to a topical product. Adult ceiling 2%, avoid in pregnancy, avoid for children.
Safe dilution matrix
Rows are the concentration, columns are the audience. Each cell carries two lines: drops per 10 ml of carrier oil, and whether this site advises that combination. Figures come from 1 ml = 20 drops, and the bold row is the ceiling for this oil.
| Dilution | Per 30 ml | Adult | Child 6+ | Pregnancy | Pets |
|---|---|---|---|---|---|
| 0.5% | 3 | 1 drops ✓ advised | 1 drops ✗ not advised | 1 drops ✗ not advised | 1 drops ✗ not advised |
| 1% | 6 | 2 drops ✓ advised | 2 drops ✗ not advised | 2 drops ✗ not advised | 2 drops ✗ not advised |
| 2% | 12 | 4 drops ✓ advised | 4 drops ✗ not advised | 4 drops ✗ not advised | 4 drops ✗ not advised |
What each concentration is normally for: 0.5% — Facial blends, sensitive or broken skin, children 6-15, first patch test · 1% — Everyday adult body and massage blends, daily leave-on use · 2% — Short-term localised adult use, 7 to 10 days then re-assess · 3% — Adult ceiling for robust oils, small area, short course only
Contraindications & handling
✓ no restriction · ! caution · ✗ avoid. An avoid row means choosing a different material, not lowering the concentration.
- ✗ Pregnancy & breastfeeding — avoid
- ✗ Children under 16 — avoid
- ! Households with pets — caution
- ! Epilepsy — caution
- ✓ Antihypertensive medication — ok
- ! Anticoagulant medication — caution
Four-step skin patch test
- Dilute 1 drop in 5 ml of carrier oil (1%).
- Apply 2 drops to the inner forearm.
- Cover for 24 hours.
- Read at 24 and 48 hours. Anethole is a mild sensitiser in a minority of people; a positive here tends to extend to anise and star anise as well.
Botanical record
- Family
- Apiaceae · Apiaceae
- Botanical part
- seed
- Extraction
- steam-distillation
- Origin
- Spain, Egypt, Bulgaria, France
- Chemotype
- trans-Anethole / fenchone type (dulce = low fenchone)
- Phototoxicity
- No phototoxicity
- Shelf life
- 24 months
Principal constituents
- trans-Anethole 68%
- Fenchone 6%
- Estragole 4%
- alpha-Pinene 3%
- Limonene 3%
- Anisaldehyde 2%
Storage & oxidation
Anethole is a phenylpropanoid rather than a terpene, and it is comparatively stable; the 3% limonene fraction is the part that oxidises. Two years is fair. Anisaldehyde gives the oil its sweet top note and also participates in the slow darkening that makes old fennel look brownish — the smell going flat is the better cue.
Rotation & substitution
Fennel is a phenylpropanoid oil and does not share a slot with the terpene oils; it should be rotated with anise and star anise excluded rather than included, because all three carry anethole. Rotate it with a citrus or a wood instead, and keep total exposure short.
Adjacent materials
Bitter fennel (Foeniculum vulgare var. amara)
15-25% fenchone instead of 6%