Is Bishop's Weed Poisonous? Toxicity to Pets and People

Bishop’s weed is toxic to dogs, cats, horses, and people. The plant (Ammi majus, also called greater ammi or false Queen Anne’s lace) contains furanocoumarins - compounds that cause serious photosensitization when the plant is ingested or when plant sap contacts skin that is then exposed to sunlight. The result can be severe burns and blistering. If your pet has eaten or contacted this plant, seek veterinary guidance promptly.

What Makes Bishop’s Weed Dangerous?

The toxic compounds are furanocoumarins, specifically bergapten and xanthotoxin (also called methoxsalen). These psoralen derivatives react with UV light to damage skin cells and mucous membranes. The seeds carry the highest concentration, but all parts of the plant are considered toxic, including the leaves, stems, and flowers.

Furanocoumarins cause two types of harm: internal irritation from ingestion, and phototoxic skin damage from sap contact followed by sun exposure.

Symptoms of Bishop’s Weed Exposure

Dogs and cats: Oral irritation, drooling, vomiting, and difficulty swallowing from ingestion. The more serious concern is photosensitization - once the plant is ingested and the animal goes outdoors, UV light triggers skin inflammation, ulceration, and exudative (weeping) dermatitis, particularly on areas with thinner fur or exposed skin. Horses develop similar photosensitization, and cases of livestock toxicity have been documented in the veterinary literature.

Humans and children: Skin contact with plant sap followed by sunlight exposure causes phytophotodermatitis - a phototoxic reaction producing redness, blistering, and in serious cases, severe burns. The reaction typically appears 12 to 36 hours after exposure. Ingesting concentrated preparations of bishop’s weed - such as herbal extracts used medicinally for vitiligo - combined with sun exposure has caused documented cases of severe phototoxic dermatitis.

What to Do

If your pet has eaten bishop’s weed:

1. Contact your vet immediately.
2. Keep the animal indoors and out of direct sunlight until you have veterinary guidance.
3. Call ASPCA Poison Control at 888-426-4435 if you cannot reach your vet.
4. Do not induce vomiting without professional direction.

If plant sap contacted human skin:

1. Wash the area thoroughly with soap and water immediately.
2. Keep the skin covered and out of sunlight for at least 24 to 48 hours.
3. Call poison control at 1-800-222-1222 (US) if a phototoxic reaction develops.
4. Seek medical care for any blistering or burns.

If a child ingested the plant:

1. Call poison control at 1-800-222-1222 (US) immediately.
2. Keep the child out of sunlight.

A Note on Confusion With Other “Bishop’s Weed”

The name bishop’s weed is applied to more than one plant. Aegopodium podagraria (ground elder) is also called bishop’s weed and is a common invasive garden plant in the UK and Europe. Ammi majus is the species with the significant furanocoumarin content and documented toxicity cases in livestock and humans. When handling any lacy white-flowered umbelifer, treat it with caution - several plants in the carrot family (Apiaceae) contain furanocoumarins to varying degrees.

Safe Handling

• Wear gloves and long sleeves when handling Ammi majus in the garden.
• Do not touch your face or eyes after handling the plant.
• Wash skin with soap and water promptly after any contact with the plant.
• If growing bishop’s weed ornamentally (it is sometimes used as a cut flower or garden annual), keep pets and children away from it.
• Dispose of cuttings and fallen seeds carefully so pets and children cannot access them.

Frequently Asked Questions

Is bishop’s weed the same as Queen Anne’s lace? They look similar but are different plants. Ammi majus is a closely related species in the same family. True Queen Anne’s lace is Daucus carota. Both contain furanocoumarins, though concentrations vary. Treat all lacy white umbel flowers with caution until you can positively identify them.

My dog ate some bishop’s weed. Is this an emergency? Yes - contact your vet or ASPCA Poison Control at 888-426-4435 immediately, and keep the dog indoors and away from sunlight until you have guidance.

Can bishop’s weed burns be treated at home? Minor redness from skin contact may be managed by washing and covering the skin. Blistering or extensive burns require medical attention. Do not lance blisters yourself.

Is bishop’s weed used medicinally? Yes - furanocoumarins from Ammi majus have been used in phototherapy for vitiligo and psoriasis. Medical use involves controlled doses and monitored UV exposure under clinical supervision. This does not make the plant safe outside that setting.

Why is photosensitization a bigger concern than direct ingestion? Because the skin damage from photosensitization can be severe even when the amount ingested is relatively small. An animal or person who ingests the plant and then goes outside may develop burns across large skin areas. Keeping pets indoors after potential exposure is the most important immediate step.