Ashley Braun, MPH, RD, is a registered dietitian and health content writer with over 5 years of experience educating patients on chronic diseases using science-based information.

Jurairat J. Molina, MD, MBA is a board-certified allergist who has been practicing in field of allergy and clinical immunology for the past two decades. 

Nightshades are foods in a family of flowering plants that go by the Latin name Solanaceae. The family includes some types of trees, vines, herbs, and crops. Many nightshade plants are popular foods in most cultures, including tomatoes, potatoes, and peppers. But they also contain high levels of substances called alkaloids that may cause health problems.

It's not common, but some people have an allergy or sensitivity to nightshades. There is also some concern that these vegetables may contribute to inflammatory conditions, like arthritis.

This article discusses the health impacts of nightshade foods and how to determine if you have an allergy.

Most of the concern about nightshades appears to focus on a substance called alkaloids.

Alkaloids are a type of phytochemical, which is a naturally occurring compound produced by plants, especially plants in the nightshade family. This compound has long been studied because of its effects on the body and potential uses for medications, drugs, and poison.

Plants produce alkaloids to protect themselves from mold, disease, and pests. The common types of alkaloids found in plants are:

Most people experience no negative health effects after eating nightshades because the alkaloids are eaten in small amounts relative to body size.

However, the concentration of alkaloids is higher in the stems, leaves, and unripe vegetables. Some research claims eating a large number of green potatoes or potato tops may lead to toxicity.

While uncommon, some people may experience sensitivities or allergies to the alkaloids in nightshades. A food sensitivity is a chemical reaction to a food and doesn’t involve an immune response, while an allergic reaction is triggered by your immune system, which falsely detects a harmless food as something harmful.

In addition, some people may experience an allergy to the fruit or vegetable itself instead of the alkaloid.

While some nightshade plants may contain higher amounts of alkaloids, they also contain other vitamins and minerals important for your overall health and well-being. For example, tomatoes contain the compound lycopene , which may help lower heart disease and cancer risk.

Here are some of the most popular nightshade fruits, vegetables, and spices:

People with an allergy to nightshades may experience symptoms after eating a food from the nightshade family, like:

An allergy is different from a food sensitivity or intolerance. Symptoms of an allergy occur when your immune system reacts to a harmless substance, such as a food. On the other hand, sensitivities and intolerances cause a chemical reaction in your body when you eat a certain food. Symptoms are not caused by an immune system response.

Sensitivity and intolerance symptoms tend to be less severe than an allergy. The symptoms primarily affect the digestive system. A nightshade intolerance may cause symptoms such as:

Despite the health claims that nightshades increase inflammation and may aggravate an autoimmune disease (a condition in which the immune system mistakenly attacks the body), the research is still limited to support these claims.

One autoimmune condition that has been researched reagarding nightshades is inflammatory bowel disease (IBD). IBD is a pair of conditions (Crohn's disease and ulcerative colitis) characterized by inflammation in the digestive system, particularly the small and large intestines.

A mouse study suggested nightshade vegetables may increase intestinal inflammation and worsen IBD symptoms. One drawback to this study is that researchers used a larger proportion of alkaloids in the mice than the average person would take in from food. So, it’s unclear if smaller doses cause the same increase in inflammation.

Some research suggests that increases in intestinal inflammation increase the likelihood for autoimmune diseases to develop. So, if nightshade vegetables do increase inflammation, they may raise the risk for autoimmune diseases such as rheumatoid arthritis, celiac disease, and Hashimoto’s disease.

While there isn’t enough research to determine if nightshade compounds cause or worsen autoimmune diseases, if you are concerned, you may wish to consider reducing them to see if this decreases your symptoms.

Nightshades are listed as foods to avoid in the Autoimmune Protocol Diet because they may worsen symptoms. This diet is a modification of the Paleolithic diet (focusing on whole foods and non-processed meats) and begins with the elimination of specific foods. However, the effect isn’t scientifically proven.

With any food allergy, you’ll want to start keeping a journal to track any patterns you notice among your diet, your lifestyle, and your symptoms. Nightshade allergies are rare, so you’ll also want to look at more common allergens, like dairy, nuts, seafood, soy, and gluten.

Your healthcare professional may recommend allergy tests to help diagnose a specific allergy, such as:

The typical treatment plan for food allergies involves avoiding foods containing the allergen. Your healthcare professional may ask you to keep a food journal to monitor your symptoms and any potential symptom triggers.

The treatment plan may also include medications to counter allergic reactions when exposed. Common medications that may be prescribed include:

Substituting other foods for nightshades can be simple when you know the right fruits and vegetables to use. Here are some easy swaps for popular nightshade foods:

A nightshade allergy is an immune response to the compound in nightshade plants called alkaloids. Types of nightshade plants include potatoes, tomatoes, peppers, red pepper flakes, eggplant, and paprika.

Symptoms of a nightshade allergy include congestion, skin rash, itching, redness, and digestive problems. Food allergies are diagnosed with a skin prick test or blood allergy test. They are treated by avoiding the allergen and medications to reduce the immune response.

A nightshade allergy isn't common. Still, people who are sensitive to it could experience bothersome symptoms and increased inflammation. If you are sensitive to nightshade foods, there are options for substituting these foods. Talk with your healthcare professional if you believe you have a food allergy. They can help determine if you do have an allergy and which foods to avoid.

No, nightshades aren’t necessarily bad for you. Some people with allergies, intolerances, or autoimmune diseases may experience adverse reactions when eating nightshades, but there is limited research to support these effects.

Alkaloids are most concentrated in nightshades like potatoes, tomatoes, and eggplant.

Many nightshade vegetables are high in vitamins, minerals, fiber, and antioxidants beneficial to health. For example, tomatoes contain lycopene, which helps protect against heart disease and cancer.

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Zang EH, Li QY, Xu JF, et al. [A preliminary pharmacophylogenetic study of Solanaceae medicinal plants containing tropane alkaloids]. Zhongguo Zhong Yao Za Zhi. 2021;46(17):4344-4359. doi:10.19540/j.cnki.cjcmm.20210623.103.

Imran M, Ghorat F, Ul-Haq I, et al. Lycopene as a natural antioxidant used to prevent human health disorders. Antioxidants (Basel). 2020;9(8):706. doi:10.3390/antiox9080706

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