It is possible that eating tomatoes, which are part of the nightshade family, could trigger an arthritis flare-up, explains About.com. However, there has been no research to show that tomatoes definitively cause arthritis pain as of 2015.
Other members of the nightshade family that may also trigger arthritis to flare up include potatoes, eggplant, peppers and ground cherries, according to About.com. Tomatillos, huckleberries and pimentos may also cause a flare-up. What may cause a flare-up in one person may not cause one in another, so there is no reason to avoid any of these foods unless the arthritis sufferer suspects that they are the cause.