Unripe green tomatoes should not be eaten. According to ultraviolet spectrophotometry, unripe tomatoes, potato sprouts, and green wheat have the same toxicity, all containing a glycoalkaloid (solanine). Eating these green tomatoes often causes discomfort, especially a bitter taste in the mouth. In severe cases, symptoms of poisoning such as dry mouth, numbness, nausea, vomiting, and diarrhea may occur. When the tomatoes ripen and turn red, the glycoalkaloid is hydrolyzed by the increased acid in the tomato itself, forming tomatidine and sugar, making them taste both sour and sweet.