The tomato plant belongs to the large Solanaceae family, commonly called the nightshade family. The leaves, stems, and green, unripe fruit contain substances that can be harmful to humans and pets. While these compounds mean the vines are technically poisonous, the actual risk level for serious injury is generally considered low.
The Compound Responsible for Toxicity
The primary toxic agent found in the foliage of the tomato plant is a glycoalkaloid compound called \(\alpha\)-tomatine. Tomatine is concentrated most heavily in the plant’s green parts, particularly the stems and mature leaves. Unripe green tomatoes also contain significant levels of this compound, which diminishes as the fruit matures and turns red.
The toxicity arises from the compound’s ability to disrupt cell membranes within the body. This disruptive action mainly irritates the gastrointestinal tract, leading to digestive upset. Tomatine is generally regarded as causing less toxic effects to mammals compared to other glycoalkaloids like solanine found in potatoes.
Risk Assessment for Humans and Pets
For humans, the risk of serious poisoning from accidental ingestion of tomato vines is small, and no acute toxicity has been reported. The leaves and stems are intensely bitter and fibrous, making it difficult to consume the large quantities needed to reach a toxic threshold. Symptoms of severe toxicity, which are rare, would include gastrointestinal distress, weakness, and confusion.
The risk is slightly elevated for household pets, especially dogs and cats, who may chew on garden plants. When pets ingest tomato foliage, the most common effects are mild to moderate gastrointestinal symptoms. These may include vomiting, diarrhea, excessive drooling, and general lethargy.
The concentration of \(\alpha\)-tomatine required to cause severe harm is high, and the bitter taste usually discourages pets from eating enough. Serious cases involving weakness, tremors, or dilated pupils are possible, but pet death from tomato poisoning is extremely unlikely. Mild stomach upset is the most probable outcome.
Practical Safety and Handling
Gardeners should be aware that the concentration of \(\alpha\)-tomatine changes dramatically as the tomato plant matures and the fruit ripens. The compounds break down as the fruit turns from green to red, rendering the mature, red tomato safe for consumption. This means the primary concern is focused entirely on the green parts of the plant and any unripe fruit.
To mitigate risk, especially for pet owners, proper disposal of pruned vines and leaves is recommended. These cuttings should be composted in a secured bin or removed from the garden area entirely to prevent dogs or cats from accessing and chewing them. While direct skin contact is not typically dangerous, those with sensitive skin should consider washing their hands after handling large amounts of the foliage to remove any plant sap residue.
If a pet is observed consuming a significant amount of the foliage or begins exhibiting severe symptoms such as persistent vomiting, extreme lethargy, or tremors, veterinary attention should be sought immediately. Quick action allows for supportive care, which is highly effective in managing the effects of glycoalkaloid ingestion.