Chronic idiopathic urticaria (CIU) is the medical term for someone who has hives for six weeks or more with no known underlying cause. Symptoms can come and go for months or even years.

While many people think that hives are always an allergic reaction to something specific, this isn’t the case with CIU. Exercise, stress, heat, cold, pressure, or a variety of other factors can trigger flares. They can also appear spontaneously, triggered by what seems like nothing at all.

Even though CIU isn’t an allergic reaction, adjusting your diet may provide relief from your symptoms. At the moment, there isn’t much concrete evidence about the effects of particular diets for CIU symptoms. Still, some limited trials show that dietary changes may help relieve symptoms, at least on an individual level.

Here are some possible diets and foods that may help you manage your CIU symptoms.

High levels of histamine may play a significant role in CIU, since many people with the condition respond well to antihistamine medications. For the 40 percent of people who don’t respond to antihistamines, though, trying an antihistamine diet may be a worthwhile next step.

In a recent study, 22 people with chronic urticaria restricted histamine-rich foods for four weeks. There was a statistically significant decrease in participants’ urticaria severity scores. Blood samples from patients in the same study showed that the level of histamines in their blood had also decreased after four weeks on the antihistamine diet.

The following foods are low in histamines and may help you manage your symptoms:

  • most vegetables
  • fresh meat
  • bread
  • pasta
  • rice
  • dairy products other than cheese and yogurt
  • certain varieties of fresh fish, including salmon, cod, and trout

You may want to consider avoiding the following foods that are high in histamines.

  • cheese
  • yogurt
  • preserved meats
  • fruits such as strawberries and cherries
  • spinach, tomatoes, and eggplant
  • alcoholic beverages
  • fermented foods
  • fast food
  • canned, frozen, and smoked fish, including tuna, anchovies, and sardines
  • seasonings such as chili powder, cinnamon, cloves, and vinegar

This list isn’t exhaustive, and the amount of histamine from dietary sources can vary.

Some foods, beverages, additives, and drugs are also theorized to either aid in the release of histamine or inhibit the enzymes needed to break it down. A few examples of these include:

  • citrus fruits
  • nuts
  • alcoholic beverages
  • teas
  • egg whites
  • food additives
  • some preservatives
  • medications such as aspirin and nonsteroidal anti-inflammatory drugs or isoniazid and doxycycline

Even if a person tests negative for food allergies, it’s possible they may be hypersensitive or intolerant to certain foods. Eating these pseudoallergens can result in reactions that resemble a true allergic reaction, including hives.

With this in mind, some doctors may recommend that people with CIU try a pseudoallergen elimination diet. This involves avoiding certain potential pseudoallergens for several weeks and slowly reintroducing them. Some examples of pseudoallergens include:

  • food additives
  • histamine
  • natural substances in fruits, spices, and vegetables

In one study, approximately 1 in 3 patients with CIU responded positively to a pseudoallergen-free diet. However, there haven’t been any randomized controlled trials to draw conclusive evidence about the diet’s effectiveness on a greater scale.

If you think your diet plays a role in your CIU symptoms, talk to your doctor about your options. They can safely help you figure out which foods to cut from your diet. A person’s tolerance to histamine is unique; therefore, it’s very important to individualize the diet plan.

You might also find it useful to keep a journal to track your symptoms after each meal. Take notes that include the specific foods you ate, what time you ate them, and how soon after your symptoms got worse or better. Share your findings with your doctor so you can work out a plan together.

Everyone reacts to foods differently. One type of diet may work for someone else, but it may not work for you. Before trying a new diet, talk to your doctor. They can help you understand what to do based on your personal circumstances.

There still isn’t much evidence that adopting certain diets can consistently and significantly affect your CIU symptoms. However, the low risk and low cost of doing so can make dietary changes worth a try.