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Pencil cactus and crown of thorns: toxicity, first aid and care
Pencil cactus and crown of thorns (Euphorbia tirucalli, Euphorbia milii): toxic for cats, toxic for dogs, toxic for small children. The toxic principle, the signs, what to do, and how to grow it.
Cats: ToxicDogs: ToxicChildren: Toxic
Also sold as: Firestick, milk bush, Christ plant.
This is a reference table, not a diagnosis and not veterinary or medical advice. It cannot tell you how much of a plant matters for a particular child or a particular animal — that depends on body weight, on the part eaten and on how long ago. If a person or an animal has eaten part of a plant, phone the poison information centre or a clinician; do not wait for symptoms, and do not make anyone vomit unless you are told to.
What is in it
Toxic principle: Diterpene esters in the milky latex — Caustic and irritant latex.
Every euphorbia bleeds a white latex, and in these two it is aggressively caustic. On skin it burns and blisters; in the mouth and gut it causes intense irritation; in the eye it causes severe chemical keratoconjunctivitis, and eye injuries from euphorbia sap are a recognised entry in the ophthalmology literature, occasionally with lasting damage.
What it looks like when it goes wrong
Immediate burning, redness and blistering of skin; drooling, vomiting and oral pain after chewing; severe eye pain, watering, light sensitivity and blurred vision after sap contact with an eye.
What to do
For an eye, irrigate immediately with plenty of clean lukewarm water for at least fifteen minutes and get seen the same day — this is the one exposure on this page that is a genuine ophthalmic emergency. For skin, wash thoroughly with soap and water. For a swallowing animal, rinse the mouth and phone a veterinary clinic. Always wear eye protection and gloves when pruning.
| Country | Poison information centre | Number | Hours |
|---|---|---|---|
| Estonia | Mürgistusteabekeskus (Health Board) | 16662 | Round the clock; 112 for an emergency |
| Finland | Myrkytystietokeskus (HUS) | 0800 147 111 | Free, round the clock |
| Latvia | Saindēšanās un zāļu informācijas centrs | 67042473 | Round the clock |
| Sweden | Giftinformationscentralen | 010-456 67 00 | Non-urgent advice; 112 in an emergency |
| Norway | Giftinformasjonen | 22 59 13 00 | Round the clock |
| Denmark | Giftlinjen (Bispebjerg Hospital) | 82 12 12 12 | Round the clock |
Anywhere in the European Union, 112 reaches emergency services and can put you through. Lithuania's poison information bureau (Apsinuodijimų kontrolės ir informacijos biuras) publishes its own round-the-clock line; if you do not have it to hand, use 112. For an animal, your own veterinary clinic or its out-of-hours service is the first call — human poison centres do not advise on animals in every country.
How to grow it
| Condition | What it wants |
|---|---|
| Light | Full sun; the firestick colour depends on it |
| Water | Sparse — treat it as a succulent |
| Temperature | 15-27 °C; frost-free and dry in winter |
Both are easy given sun and neglect. Crown of thorns flowers almost continuously in a bright window and is a genuinely rewarding plant, thorns aside. Pencil cactus grows fast and needs pruning, which is exactly the operation that puts sap on your hands — do it outdoors, with gloves and glasses, and stop the bleeding cut with cool water.
What it gets confused with
It is sold as a cactus and it is not one; that matters because people prune "cacti" without a second thought and cacti do not bleed. Poinsettia is in the same genus and has a much milder latex, which is why one euphorbia has an undeserved reputation and another has an under-appreciated one.
A plant that is not on the toxic lists
If you are deciding what to keep in a home with a cat, a dog or a small child, this one fills a similar role and is not flagged by the veterinary services.
Others that work the same way
Caustic and irritant latex — these behave alike, and what you would do about them is alike too.
Poinsettia
Mildly irritant milky latex
Weeping fig and rubber plant
Milky latex containing ficin and related irritants
Source: ASPCA Animal Poison Control — toxic and non-toxic plants · checked 2026-09-06
Care guidance is standard horticultural practice for a cool-temperate northern climate. Poison-centre numbers are listed on the hub page and are worth confirming against your own country's health service.
Frequently asked questions
Is pencil cactus toxic to cats?
The veterinary lists rate it "toxic" for cats and "toxic" for dogs. The toxic principle is diterpene esters in the milky latex. Every euphorbia bleeds a white latex, and in these two it is aggressively caustic. On skin it burns and blisters; in the mouth and gut it causes intense irritation; in the eye it causes severe chemical keratoconjunctivitis, and eye injuries from euphorbia sap are a recognised entry in the ophthalmology literature, occasionally with lasting damage.
What should I do if my dog eats pencil cactus?
For an eye, irrigate immediately with plenty of clean lukewarm water for at least fifteen minutes and get seen the same day — this is the one exposure on this page that is a genuine ophthalmic emergency. For skin, wash thoroughly with soap and water.
Is pencil cactus dangerous for a small child?
The verdict for a child who chews or swallows part of it is "toxic". Immediate burning, redness and blistering of skin; drooling, vomiting and oral pain after chewing; severe eye pain, watering, light sensitivity and blurred vision after sap contact with an eye.
How do you care for pencil cactus?
Light: Full sun; the firestick colour depends on it. Water: Sparse — treat it as a succulent. Temperature: 15-27 °C; frost-free and dry in winter. Both are easy given sun and neglect. Crown of thorns flowers almost continuously in a bright window and is a genuinely rewarding plant, thorns aside.
What is pencil cactus confused with?
It is sold as a cactus and it is not one; that matters because people prune "cacti" without a second thought and cacti do not bleed. Poinsettia is in the same genus and has a much milder latex, which is why one euphorbia has an undeserved reputation and another has an under-appreciated one.
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