Do tomatoes contain something that worsens arthritis?

Depends. Some people have food sensitivities to tomatoes. The only way to know for sure if a certain type of food increases your joint pain is to eliminate it from your diet. If the symptoms go away or get better you ca reintroduce the food and see if the symptoms return.
Lycophene is . Found in tomatoes and has actually been theorized to have anticancer and in some forms anti inflammatory effects but there are some who may have allergens to certain foods and have an inflammatory related arthrits or arthridite and tomato may have an allergen for those specific individuals thus the arthritis tag..But lycopenes have huge benefits. In general fresh tomatoes are good foods.