Milkweed (plants in the Asclepias genus) is widely recognized as the sole host plant for Monarch butterfly caterpillars. Concern regarding contact with this plant stems not from the leaves or flowers, but from the milky white fluid, known as latex or sap, that exudes when the plant is damaged. This sticky sap contains natural defense chemicals that can cause adverse reactions upon contact with human skin or mucous membranes.
Identifying the Toxic Component
The milky sap that flows from a broken milkweed stem is a form of latex containing a high concentration of natural toxins called cardiac glycosides. These compounds, more specifically referred to as cardenolides, represent the plant’s primary defense mechanism against most grazing herbivores. The latex causes a stronger enzymatic inhibition than the cardenolides found within the plant’s leaves, signifying a greater concentration of potent compounds in the sap.
Cardenolides act as inhibitors by interfering with the sodium pump (\(\text{Na}^+/\text{K}^+\)-ATPase) found in animal cells. This pump regulates the concentration of sodium and potassium ions across the cell membrane, a process foundational to the function of nerve and muscle cells, including the heart. By disrupting this mechanism, the toxins offer the plant protection, making the tissues unpalatable and potentially toxic to most animals.
Common Skin Contact Symptoms
Direct exposure of the skin to milkweed sap typically results in a localized dermal reaction, often described as contact dermatitis. Immediate effects can include irritation, redness, and a burning sensation, particularly in sensitive individuals. Because the sap contains irritating substances, it can lead to symptoms like itching or the formation of mild blistering in the affected area.
The severity of the reaction depends on the amount of sap involved and the individual’s sensitivity. Even a small smear of the thick, sticky fluid can cause noticeable discomfort. If contact occurs, the affected area should be washed immediately and thoroughly with soap and water to remove the irritating latex. Wearing gloves when handling milkweed, especially when cutting or pruning, is a simple precautionary measure that can prevent this common type of exposure.
Failing to wash hands after contact can lead to secondary exposure on other parts of the body, such as the face or arms. Although milkweed sap is not generally considered a severe skin hazard like poison ivy, prompt decontamination is the best way to minimize the duration and intensity of the localized irritation. Any persistent pain, widespread rash, or worsening skin reaction should prompt a medical examination.
Severe Exposure and Necessary First Aid
Exposure to the eyes or accidental ingestion represents a more concerning level of contact due to the potency of the cardenolides. If milkweed sap gets into the eyes, it can cause immediate and intense burning and stinging, leading to inflammation and redness. Ocular exposure can lead to corneal endothelial toxicity, which affects the inner layer of the cornea and may result in light sensitivity, blurred vision, and significant pain.
Symptoms of eye exposure may not always appear instantly, sometimes being delayed for hours, which can confuse the source of the irritation. The primary action is to immediately rinse the eye with lukewarm running water for 10 to 15 minutes to dilute and wash away the sap. Following irrigation, a medical professional, such as an ophthalmologist, should be consulted for a full examination and treatment, which often includes steroid eye drops to manage swelling and inflammation.
Accidental ingestion of milkweed plant material, which is much less common than dermal exposure, introduces cardenolides into the body’s systemic circulation. Ingestion symptoms typically appear within a few hours, beginning with gastrointestinal distress, including nausea, vomiting, abdominal pain, and diarrhea. Systemic toxicity can progress to neurological symptoms like lethargy, confusion, and dizziness. It can also affect the heart, causing changes in heart rhythm and a decreased heart rate. Anyone who ingests milkweed or experiences severe symptoms after contact should immediately contact Poison Control for guidance on emergency care and observation.