Crown of thorns (Euphorbia milii) is a succulent, cactus-like plant that is native to Madagascar. It’s adaption to warm temperatures year round makes it an ideal houseplant, and it is also grown as a garden flower in Florida and other Southern states. The name comes from a legend associating the plant with the crown of thorns worn by Christ in the Bible. The plant has sharp pointed thorns about ½ inch long. It grows to be about 1-2 feet (30-60 centimeters) tall normally, but consistent warm temperatures can make it bigger. The flowers are usually bright red, pink or white. Like all members of the Euphorbia family, crown of thorns flowers grow in a cyathium, a cluster of minimally developed male and female flowers. In E. milii the cyathium appears as a group of small stems surrounded by two large petal-like bracts.

Euphorbia species, often called spurges, are toxic to humans and pets. Poisonous chemicals are strongest in the milky white sap that is referred to as latex, but any part of the cut plant can cause symptoms. One of the toxins has been identified as phorbol esters, a chemical which can affect protein and enzyme production throughout the body. Skin contact with the latex causes irritation while ingestion leads to gastrointestinal upset with vomiting and bloody diarrhea. Phorbol esters also has carcinogenic properties that promote tumor formation. Crown of thorns has a bitter taste that is unpleasant to dogs, so ingestion is rare, and the thorns also help to keep animals from getting too close. A skin wound from one of the thorns will not cause poisoning, although care should be taken to keep it from becoming infected. However broken stems or leaves with leaking sap can cause skin irritation and dermatitis upon contact. Inflammation is most painful in the mucous membrane of the mouth, eyes, and nose, and severe eye exposure can lead to vision loss and blindness.

Crown of thorns is a southern garden plant that is often grown as a houseplant in colder climates. The plant has a milky white sap that is toxic to humans and dogs. Skin contact causes irritation and dermatitis. Gastrointestinal symptoms are associated with ingestion.

These are the symptoms you may see if your dog is exposed to crown of thorns. All severe symptoms should be treated by a veterinarian.

There are many different varieties of crown of thorns all of which could cause poisoning in your dog. Additionally, there are also other species of Euphorbia which might cause similar symptoms. The best known are Euphorbia pulcherrima, the very common Poinsettia plant, and Euphorbia marginata, (snow-on-the-mountain).

There are a number of risk factors which will make crown of thorns poisoning more likely.

Crown of thorns poisoning will be diagnosed based on symptoms and a history or ingestion or contact with the plant. Finding broken stems on a houseplant should concern dog owners even if the plant doesn’t appear chewed, since the sap alone can cause irritation to the skin. If you think your dog may have eaten or come in contact with crown of thorns sap, you should call a veterinarian or poison helpline and ask for advice. Ingestion of a large amount is rare, but it can be quite serious and sap in the eyes could cause blindness. If the veterinarian asks to see your dog, bring a sample of the plant for identification. Handle the plant with gloves when cutting and transport the sample in a sealed bag.

The veterinarian will examine your dog for physical symptoms and signs of inflammation on the mouth or eyes. A thorough eye examination may be necessary to evaluate whether there is permanent damage. Blood and urine tests can help to determine the severity of toxicity if you think your dog may have ingested crown of thorns. These tests can also help to rule out other potential causes if you’re not sure what happened.

In the case of topical exposure, the first treatment will be to remove traces of latex from the skin. Crown-of-Thorns’ sap is not water soluble, but it can be washed off with milk or a small amount of mild soap. Gently clean the affected area to remove as much of the toxins as possible. If your dog ingested the plant, give him milk or water to drink.

If symptoms are very severe, the veterinarian will prescribe medication to reduce inflammation in the eyes, mouth or nose. You may be referred to an eye specialist if there is severe damage to the eyes. Eye drops may need to be applied frequently during the healing process. Other areas of affected skin will be treated topically. Medication may be given to protect the stomach and intestinal lining if the sap was ingested.

There is a high chance of recovery from crown of thorns poisoning. Most symptoms are limited to mild dermal exposure and the dog will recover easily once the sap is removed. Eye exposure could result in permanent vision loss or blindness which would need to be managed with re-training and lifestyle adjustments.

To reduce the risk of exposure, keep all crown of thorn plants out of reach of your dog and train him to avoid them if possible. Take precautions any time you’re are cutting or pruning the plant. Keep your dog out of the way and ensure proper ventilation for yourself and anyone nearby. Sap vapors carried in the air have been known to cause eye and throat irritation when the plant is cut in greenhouses, so this is very important. Wear gloves whenever handling the plant and put any cuttings you’re are throwing away in a garbage can your dog cannot access.