When potatoes grow purple buds, they will produce a harmful substance called solanine. Solanum nigrum is a toxin, which is harmful to human health. Potatoes stored for a long time or improperly stored are prone to produce purple buds, which indicates that potatoes have gone bad. Solanum nigrum can cause gastrointestinal reactions, such as itchy throat, nausea and vomiting, abdominal pain, etc., which can lead to serious poisoning symptoms, such as tinnitus, loss of consciousness and even death.