What would be causing Hives?

I break out in hives after eating tomato sauce and running. What is causing this?

• In the course of one month, I have broken out in hives 3 times! The first time, I had pizza and I went to the gym 2 hours later for a 20 minute run. After running, my body started feeling itchy and I noticed I was breaking out in hives all over. The second time, I had spaghetti and meatballs; again I went to the gym 2 hours after eating and the same thing happened. So I assumed it was a certain brand of sauce. Yesterday, I went out and had pizza at a place that has been using the same recipes forever! I've eaten there a few times and never had any issues. It was raining really hard, so I decided to run back to my friend's office. I broke out in hives and well, it was a brisk run of maybe less than 10 minutes. It was not as long lasting as the other two. So, now I've identified the actions that cause my body to react, what is causing my body to react this way? What could it be?

• Answer:

  I was never allergic to cats until around the time I turned 20. Allergies can be triggered along your lifetime. You're probably generally mildly allergic to tomatoes, but the allergy becomes a topical skin issue when you sweat. I'm also allergic to tomatoes, but instead my mouth gets itchy after I eat them. It goes away after about an hour. Another possibility is that you have triggered a histamine reaction to your laundry detergent if the rash is occurring where your clothings lies. Sweating can exacerbate this. Try taking some Diphenhydramine (anti-histamine) before you workout or see your doctor for a prescription allergy medication.