Some vendors use the method of ripening bananas to ripen tomatoes, applying a chemical substance called "ethephon" to them. Although this substance has low toxicity, long-term consumption is harmful to the human body.
Ripened tomatoes are often sold out of season, are uniformly red in size and color, feel very hard, and have a polyhedral appearance. When broken open, the seeds are green or undeveloped, and the flesh is juiceless. In contrast, naturally ripened tomatoes have some green around the stem, feel soft to the touch, have a smooth and round appearance, with tan-colored seeds, and the flesh is red, sandy, and juicy.