Nightshade Allergy 101

Plants produce a number of chemical compounds for their own use, and it just so happens many of those compounds benefit us, too. Some plant chemicals, though, can be toxic, especially for those with allergies or sensitivities. Nightshades such as tomatoes, potatoes, and peppers are packed with fiber, antioxidants, and other nutrients, but if you have a nightshade allergy or intolerance, you may need to eliminate them from your diet. In this article we’ll look at what nightshades are, why they can be problematic, and how to find out if you are allergic or sensitive to them.

What Are Nightshades?

Nightshades, members of the family Solanaceae, are flowering plants high in solanine, a naturally occurring alkaloid compound. Alkaloids are bitter nitrogen-containing compounds that are thought to be produced by plants (and a few animals) as natural pesticides.

Alkaloids are stored in varying amounts in each part of a plant, with the leaves, seeds, roots, and bark tending to have the highest concentrations. Some alkaloids, such as morphine, caffeine, and nicotine, can have biological effects, such as alertness and decreased sensation of pain, when we consume them. (Source, Source)  

Alkaloids can have biological effects on the circulatory system and the gastrointestinal tract. Some alkaloids include:

• Solanine: Found in potatoes, tomatoes, and eggplants. Solanine poisoning can occur when high levels are consumed, most commonly in the form of green potatoes. Milder symptoms may occur with low-level exposure or consumption. Neurological symptoms of solanine poisoning such as headache and even hallucinations have been reported, but most common are gastrointestinal symptoms such as vomiting, cramping, and diarrhea. (Source)
• Nicotine: Found in tobacco leaves, nicotine was once used as an insecticide in the United States. Nicotine is known to be highly addictive when consumed through tobacco products. This kind of relatively low-level exposure can cause an increase in blood pressure, heart rate, and alertness. Nicotine is extremely toxic in larger amounts, and severe exposure can lead to abnormal heart rhythm, involuntary twitching, paralysis of the muscles that control breathing, and death. (Source)
• Capsaicin: Found in peppers, capsaicin is the compound that gives spicy peppers their heat. Capsaicin may increase intestinal permeability, which means both that it may enhance delivery of oral medication and that it may play a role in leaky gut. Capsaicin may also alter the composition of the gut microbiota, and has been studied for possible use in the treatment of obesity. (Source)

Is It Safe to Eat Nightshades?

Some nightshades are toxic to humans, but many are not. Common examples of edible nightshades include:

• tomato
• tomatillos
• potato (red and white potatoes)
• eggplant and aubergine 
• bell peppers, hot peppers, chili peppers, pimiento 
• goji berries 
• ground cherries (similar to tomatillos)
• spices sourced from pepper, such as cayenne powder, chili powder, and paprika 

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There a quite a few foods that are commonly mistaken for nightshades. However, the following list of foods are not part of the nightshade family and thus would not need to be avoided if you have a nightshade allergy or sensitivity. This includes:

• sweet potato
• zucchini 
• black pepper
• cucumber
• spinach 
• garlic
• coffee

(Source, Source)

What Is Nightshade Allergy? 

Nightshade allergies are rare, but do sometimes occur. Like other kinds of allergies, food allergies involve an inappropriate immune response to something that is not otherwise harmful. Allergy symptoms can range from mild to life-threatening.

Symptoms of a nightshade allergy include:

• rashes and itching
• hives
• achy muscles or joints
• swelling of the face or other parts of the body
• excessive mucus production
• trouble breathing, nasal congestion, or wheezing
• dizziness
• constriction or tightening of the airway

(Source, Source)

What Is Nightshade Intolerance?

Slightly more common than nightshade allergy is nightshade intolerance or sensitivity, where you have trouble digesting nightshades. A food sensitivity is generally caused by a deficiency of enzymes that normally break food down a particular food.

Symptoms of food intolerance may include the gastrointestinal tract, but other parts of the body may also be affected. Often you may be able to tolerate small portions of a food that causes symptoms in larger amounts.

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Symptoms of nightshade intolerance or sensitivity may include:

• bloating and gas
• nausea
• heartburn
• diarrhea
• joint pain
• fatigue
• brain fog

(Source, Source)

How Do I Know if I Have Nightshade Allergy or Intolerance?

The first step in diagnosing a nightshade allergy or intolerance is identifying a triggering food (or foods). Keeping a food diary in which you note what you eat and how you feel afterward is a first step. An elimination diet, in which you take nightshades out of your diet completely, then add them back in one at a time until you notice symptoms, is often recommended but is not without risks.

Any elimination diet can deprive you of valuable nutrients. For some, this kind of focus on regulating intake can trigger eating disorders. In the case of a true food allergy, a severe immune reaction to a trigger food can be dangerous. And the results of an elimination diet won’t necessarily help you tell the difference between an allergy and a sensitivity. (Source)

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Not sure if nightshades are the culprit behind your inflammatory symptoms? Work with our Certified Nutritionists and Registered Dietitians to get to the bottom of it.

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Testing for Nightshade Allergy

Laboratory tests may help identify a nightshade allergy. These tests are not completely reliable by themselves, but used together with a health history and physical exam may help diagnose a possible allergy. Tests include:

• skin prick test: A small amount of a suspected allergen is placed on skin and the skin is lightly pricked or scratched to increase exposure. (Source)
• blood test: A sample of blood is checked for immunoglobulin E (IgE) antibodies, which are produced by the immune system when reacting to a specific allergen. (Source) 

How Is Nightshade Allergy Treated?

The treatment for a nightshade allergy is the same as for any other allergy — avoiding the allergen as much as possible, and using medication when necessary to relieve symptoms of exposure.

If you have been diagnosed with a nightshade allergy, you consult with your health care provider and come up with a plan in case you have an allergic reaction. Depending on how severe your allergy is, treatments may include:

• antihistamines
• epinephrine (injection for life-threatening reactions)
• bronchodilators (asthma inhalers)
• steroids (such as cortisone)

(Source)

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How Is Nightshade Intolerance Treated?

If you have nightshade intolerance, the only real treatment is to avoid eating the food that triggers your symptoms. In some cases you may be able to tolerate limited quantities of the food, rather than having to avoid it altogether.

If your nightshade intolerance is related to another condition, such as irritable bowel syndrome (IBS) or stress, treating that underlying condition may be your best bet. (Source)

Alternatives to Nightshades

If you’re allergic or sensitive to nightshades, you can explore alternatives such as swapping:

• potato with sweet potato, yam, cauliflower, or other root vegetables
• tomato with grape, strawberry, melon, apple, or pear
• eggplant with portobello and shiitake mushrooms
• bell pepper with celery, radish, or swiss chard
• cayenne pepper with cumin
• goji berries with blueberries

(Source)

How Do Nightshades Affect Autoimmune Conditions? 

The alkaloids in nightshades have the potential to exacerbate inflammation, irritate leaky gut, cause stress, and increase the immune response. These effects can contribute to flare-ups of existing autoimmune diseases, such as Crohn's disease, ulcerative colitis, lupus, rheumatoid arthritis, and Hashimoto's disease. (Source)

The Bottom Line on Nightshade Allergy

Nightshades can be a good source of antioxidants and other nutrients, but the alkaloids they contain can be toxic in large amounts and may contribute to inflammation, leaky gut, and autoimmune flares. If you lack the enzymes needed to digest nightshades, you may experience uncomfortable digestive symptoms when you eat them. And while it’s rare, it is possible to have a nightshade allergy that causes an immune reaction. Food diaries, elimination diets, and skin or blood testing may be helpful in identifying a nightshade allergy or sensitivity.