If you have children or pets, your houseplants may be a potential source of danger. Many plants have evolved poisons as a way to ward off potential predators. In many cases, these poisonous plants merely cause stomach upset and pain, but some are much worse. Don't assume a plant is safe just because it is sold as a houseplant; some of the most common plants are also among the most poisonous.
Many cacti and other succulents are often used as houseplants, but many of them are potentially irritating, poisonous or even lethal. Aloe, one of the most common houseplants, is used to treat burns, rashes and other skin conditions, but it has an irritating yellow latex inside its leaves, alongside the soothing, clear gel. If the latex is not washed off the gel, it can cause painful and itchy rashes. It can cause painful cramps and abdominal pain when taken internally. At the other end are euphorbias. These succulents have latex so toxic that it can cause intense itching and rashes where it touches the skin, permanent vision damage in the eyes, and death if taken internally. Do not touch any succulent or cactus around your house without using cactus gloves unless you know that it is safe to handle.
English ivy is tough, easy to grow, fast spreading and attractive, making it a popular plant both inside and outside. Although it is safe to touch, it can be quite dangerous when ingested. It is poisonous to humans as well as pets, and can cause breathing difficulty, paralysis, vomiting and convulsions and even coma. Other species of ivy such as pothos (also known as devil's ivy) and Boston ivy are also poisonous. Do not keep ivy near pets or young children unless you know your species is safe.
Lilies make popular houseplants, but many can be toxic. One of the most dangerous is the Atamasco lily or rain lily which, according to the North Carolina Cooperative Extension, can be fatal if swallowed. The bulb is the most dangerous part, but all parts of the plant are potentially hazardous. The calla lily is also a common houseplant that can be fatal if swallowed. Initial symptoms of consuming it include swelling and a painful burning sensation in the throat, tongue and lips as well as digestive complaints. The African lily, by contrast, only causes low toxicity in humans, but still can cause nausea, vomiting and diarrhea if swallowed.