Toxicology Q&A: Which Plant’s Sap Is Toxic to the Eyes?

HINT: It can cause mild conjunctivitis to severe keratouveitis and even blindness if contact occurs with your eyes.

ANSWER: Wart spurge (Euphorbia helioscopia, also known as umbrella milkweed, wartweed, or madwoman’s milk), is one of the group of plants called spurges. The term “spurge” is medieval French from epurger, referring to the purgative properties of the plant. Euphorbiaceae is one of the largest families of flowering plants and has 300 genera and more than 7,000 species.

It is an annual succulent plant that flowers from May to October and is pollinated primarily by flies. It grows in well-drained sandy or loamy soils on all five continents. It does not grow well in the shade.

The sap of the plant is a thick milky liquid, rich in alkaloids and terpenoid compounds (diterpene esters). In nature, these are used by the plant for defense against herbivores and herbivorous insects.

The primary toxic effect is to the skin and occurs via a variety of mechanisms, depending upon which genera one is touching. All parts of the plant are toxic.

A contact urticaria can occur in some of the subfamilies (Acalyphoideae and Crotonoideae) from stinging hairs. These hair complexes include a crystal spike complex, called a druse, that penetrates the skin and injects an irritant compound (undefined but causing histamine release).

Chemical irritation also can occur from contact with the milky sap during pruning or plant removal. This results in red, swollen skin lesions that can develop blistering and bullae, which may scar.

A 2005 case report by Wilken and Schempp has illustrative dermal-injury photographs showing linear facial bullae in a six-year-old exposed to the plant’s sap.1

Serious injury to the eyes can occur if the sap comes in contact or is brought in contact by inadvertent transfer (hands to eyes). These ocular reactions range from mild conjunctivitis to severe keratouveitis—there are several documented cases of permanent blindness after exposure.2

Oral ingestions can lead to painful local mucosal irritation, salivation, and swelling of the mouth and throat; acute vomiting, diarrhea, cramping, and severe abdominal pain have also been described.

There is no antidote.

If exposed, the eyes or skin should be rinsed immediately with water. A medical evaluation for eye exposures with significant symptoms is recommended.

Treatments for ingestion include dilution with water. Activated charcoal has been suggested but not validated.