Bell Peppers: Nightshades, Allergy, Pesticides, and Safety

Table of Contents

1. The Nightshade and Arthritis Belief
2. Glycoalkaloids: The Chemistry Behind the Worry
3. How to Test It Honestly on Yourself
4. Oral Allergy Syndrome and Profilin
5. True Bell Pepper Allergy and the Paprika Puzzle
6. Pesticide Residues: The Actual Numbers
7. Washing, Peeling and Organic
8. Why Sweet Peppers Have No Heat
9. The Skin, Digestion and Sensitive Guts
10. Other Practical Cautions
11. Key Research Papers
12. Connections
13. Featured Videos

The Nightshade and Arthritis Belief

Bell peppers belong to the Solanaceae, the nightshade family, with tomatoes, potatoes, aubergines (eggplant) and chillies. The idea that these foods cause or worsen arthritis has circulated since the 1970s and 1980s, when a horticulturist who believed his own joint pain came from nightshades collected testimonials from people who felt better after giving them up. It has never gone away, and it is now a fixture of "anti-inflammatory diet" advice online.

What is the evidence? Searching PubMed for controlled human studies of nightshade vegetables and arthritis finds none: no randomised trial, no controlled elimination study, no cohort in which pepper or tomato intake predicted arthritis onset or flares. The literature consists of the original testimonial collections and of reviews that mention the belief. Tedeschi and colleagues' 2017 survey of 217 people in a rheumatoid arthritis registry is the nearest thing to data: 24% said foods affected their symptoms, 15% reported improvement and 19% worsening from specific foods; blueberries and spinach were most often named as helping and sugary soft drinks and desserts as worsening symptoms. It is a survey of beliefs, and it shows that most people with RA do not perceive food as a driver at all.

The professional position follows the evidence. The American College of Rheumatology's 2022 guideline on exercise, rehabilitation, diet and other integrative interventions for rheumatoid arthritis issued 28 recommendations, three of them about diet: a conditional recommendation for a Mediterranean-style diet, and conditional recommendations against other formally defined diets and against dietary supplements for disease control. Nothing about nightshades. Skoczyńska and Świerkot's 2018 review of diet in rheumatoid arthritis likewise identifies oily fish, and the avoidance of high-sugar, high-fat processed eating, as the dietary factors with support — the same Mediterranean pattern, in which tomatoes and peppers are staples.

None of this proves that no individual reacts to peppers. It means that the population-level claim — nightshades cause arthritis — has no controlled support after fifty years, and that a blanket instruction to avoid them removes some of the most nutrient-dense vegetables in the diet on the strength of anecdote.

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Glycoalkaloids: The Chemistry Behind the Worry

The mechanistic story attached to the belief is that nightshades contain glycoalkaloids — solanine and chaconine in potatoes, tomatine in green tomatoes — which are genuinely toxic in quantity and which, the theory goes, inflame joints or disturb calcium metabolism. The chemistry is real; the leap to peppers is not.

Friedman's 2006 review of potato glycoalkaloids is the standard reference. Solanine and chaconine are concentrated in green, sprouting and damaged potatoes and in the peel; they are the reason a bitter, green potato should be discarded; and at high doses they cause gastrointestinal and neurological symptoms. That literature is about potatoes. Sweet peppers are not a meaningful source of these compounds — the alkaloid the Capsicum genus is known for is capsaicin, which sweet peppers do not make (see below) — and there is no case series of glycoalkaloid poisoning from bell peppers. A person worried about glycoalkaloids has a real reason to avoid green potatoes and no measured reason to avoid a red pepper.

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How to Test It Honestly on Yourself

Because the evidence is absent rather than negative, the only way to find out whether nightshades affect your joints is a proper elimination and re-challenge, done in a way that can actually tell you something:

• Remove all nightshades — peppers, tomatoes, potatoes, aubergine, chilli, paprika, and the tomato and paprika hidden in sauces and spice mixes — for three to four weeks, keeping everything else as constant as you can (medication, sleep, activity, the rest of the diet).
• Score your pain and stiffness daily on a simple 0–10 scale throughout. Memory is a poor instrument for this.
• Reintroduce one nightshade at a time in a normal portion for three days, watching the scores, before adding the next.
• Remember that arthritis flares and remits on its own, that most elimination diets improve how people feel for a few weeks regardless of what was removed, and that removing nightshades usually removes a lot of processed food (pizza, chips, ketchup) at the same time.

If a specific nightshade reliably and repeatedly worsens your scores on re-challenge, avoiding it is reasonable and costs little. If nothing changes, you have your answer and can put peppers back on the plate. What is not reasonable is telling other people to give them up on the basis of your result, or theirs.

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Oral Allergy Syndrome and Profilin

This is the one item on this page that will genuinely affect a large number of readers. If raw bell pepper makes your lips, tongue or throat itch or tingle within minutes, and you have spring hay fever, you very probably have oral allergy syndrome (pollen-food allergy syndrome). Price and colleagues' 2015 review describes it: a reaction to plant foods that requires prior sensitisation to a cross-reacting inhaled pollen allergen, most often birch, and that usually stays confined to the mouth because the responsible proteins are broken down by stomach acid and by heat.

In bell peppers the responsible protein is chiefly profilin. Jensen-Jarolim and colleagues (1998) tested extracts of eight horticultural strains of bell pepper against the blood of eleven bell-pepper-allergic patients. Profilin was present in every strain and bound IgE strongly in all of them, and that binding could be blocked by recombinant birch-pollen profilin (Bet v 2) — direct evidence that the pepper reaction is a birch cross-reaction. A homologue of the major birch allergen Bet v 1 turned up in four of the eight strains but mattered to only one of the eleven patients. Willerroider and colleagues (2003) cloned the bell pepper profilin, named Cap a 2, and found it 91% identical to tomato profilin; eleven of 34 food-allergic patients (32%) had IgE against both. Ebner and colleagues (1995) had earlier shown the general principle: proteins homologous to Bet v 1 and Bet v 2 are found across birch-pollen-related foods — apple, pear, celery, carrot, potato — and inhibition with the recombinant birch proteins blocks the IgE binding.

Profilin is a "panallergen": the same protein family in birch pollen, grass pollen, tomato, melon, banana, celery and pepper. So a person with pepper oral allergy will often notice the same itch from raw tomato or melon, and it tends to be worse in the pollen season. Three practical consequences:

• Cooked pepper is usually fine. Profilin is heat-labile. Roasted, stir-fried or stewed peppers are tolerated by most people who react to raw ones. The same is often true of well-cooked tomato sauce.
• The reaction is usually mild and local, but not always; a minority of profilin-sensitised people react systemically, and anyone who has had throat swelling, hives beyond the mouth or breathing difficulty from a food needs an allergist and an emergency plan, not a paragraph on a website.
• Antihistamines dampen it, and some people find peeling the pepper or choosing a different colour makes a difference, since allergen content varied between strains in the Jensen-Jarolim study.

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True Bell Pepper Allergy and the Paprika Puzzle

Genuine primary allergy to bell pepper — sensitisation to the pepper itself rather than through pollen — exists but is uncommon, and it has a curious occupational form. Vermeulen and colleagues (2003) studied greenhouse workers in the Netherlands who had become allergic to sweet bell pepper pollen: their IgE recognised pepper-pollen proteins of 14, 29 and 69 kDa that showed little or no cross-reactivity with grass, birch or mugwort pollen, so this was a primary sensitisation to the crop, not a spillover from hay fever. It is a hazard of working in a pepper greenhouse, not of eating peppers.

Paprika, the dried and ground red pepper, behaves slightly differently again. Leitner and colleagues (1998) studied patients with the mugwort-birch-celery-spice syndrome and found that their IgE reactivity to paprika and pepper (the spice, Piper nigrum, was also tested) was not explained by Bet v 1 or profilin homologues; the main paprika allergen was a 23 kDa protein related to an osmotin-like protein of tomato — the same P23 protein Jensen-Jarolim found in half the fresh bell pepper strains. Osmotin-like proteins are more heat-stable than profilin, which is one reason a small number of people react to cooked or dried pepper products even though most oral-allergy sufferers do not.

For a reader: an itchy mouth from raw pepper with hay fever is almost always oral allergy syndrome, manageable by cooking; a reaction to cooked pepper or to paprika, or any reaction beyond the mouth, deserves proper allergy testing.

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Pesticide Residues: The Actual Numbers

Bell peppers appear regularly on the annual "most contaminated produce" lists published by an environmental advocacy group, which rank foods by how often residues are detected in the US Department of Agriculture's Pesticide Data Program (PDP) sampling. Detection frequency and health risk are different things, and the difference is the whole point.

Winter and Katz (2011) took the twelve commodities on that list — bell peppers among them — and, using the PDP's own residue findings, estimated real dietary exposure to the ten most frequently detected pesticides on each, then compared each exposure with the chronic reference dose (the daily intake regulators consider safe over a lifetime, itself set with large safety margins below the level with any effect in animals). All 120 exposure estimates were below the reference dose. Only one of the 120 exceeded even 1% of it — and that one was on bell peppers: methamidophos, at 2% of the reference dose. Three-quarters of the pesticide-commodity combinations were below 0.01% of the reference dose, meaning exposures roughly a million times below the no-effect levels in animal toxicology. The authors also concluded that substituting organic for conventional versions of the twelve foods would not appreciably reduce consumer risk, and that ranking foods by detection frequency without regard to dose lacks scientific credibility.

Two honest footnotes. Methamidophos, the pepper's worst offender in that analysis, has since had its US registrations cancelled, so the current picture is better than the 2011 one. And reference doses are regulatory constructs; they are conservative, but they are set per chemical, and the science of low-dose mixtures in children is still developing. The reasonable conclusion is not that residues are zero — they are not — but that the measured exposure from eating bell peppers is a very small fraction of any threshold of concern, and far smaller than the well-documented cost of eating fewer vegetables.

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Washing, Peeling and Organic

Rinsing works, partly. Krol and colleagues (2000) grew and treated crops under normal field conditions, then compared unwashed with tap-water-rinsed samples for twelve pesticides. Rinsing significantly reduced residues of nine of the twelve; three (vinclozolin, bifenthrin, chlorpyrifos) were not reduced, because they are held in the waxy surface rather than sitting on it. The practical rule is a rinse under running water with a rub of the fingers — the friction matters more than the water — and there is no need for commercial produce washes.

Baking soda does more for surface residues. Yang and colleagues (2017), working with apples, found that a 1% sodium bicarbonate solution removed surface residues of two pesticides more effectively than tap water or a bleach solution, taking 12 to 15 minutes to clear them completely. The same study showed the limit: a systemic pesticide that had penetrated the peel (about 20% of the applied thiabendazole) could not be washed off by any method. For a bell pepper, whose smooth, waxy skin holds residues on the surface, a soak in water with a spoonful of baking soda followed by a rinse is a sensible, evidence-based routine if residues worry you.

Peeling removes essentially all surface residue and is easy after roasting, at the cost of some fibre and the skin's share of the carotenoids. Cutting away the stem end, where a pepper's crevices collect the most, is a reasonable habit.

Organic lowers exposure to synthetic pesticides. Bradman and colleagues (2015) switched 40 children in two Californian communities to an organic diet for a week: urinary markers of organophosphate insecticides fell by 40 to 49% and the herbicide 2,4-D by 25%, while several other pesticide markers were unchanged. Organic peppers are a legitimate choice for people who want that reduction; the Winter and Katz analysis suggests the health gain is small because the conventional exposure was already tiny, and organic peppers are often much dearer. If price forces a choice between organic peppers occasionally and conventional peppers often, the evidence on vegetable intake and mortality says eat the peppers.

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Why Sweet Peppers Have No Heat

Bell peppers are the same species as jalapeños and cayenne (Capsicum annuum). The reason they do not burn is a single gene. Stewart and colleagues (2005) identified the Pun1 locus, required for capsaicinoid production, as a gene encoding an acyltransferase enzyme — the one that performs the final step of joining vanillylamine to a fatty acid to make capsaicin. Every non-pungent pepper they tested carried the recessive pun1 allele, which has a deletion spanning the gene's promoter and first exon, so the enzyme is never made. Sweet peppers are not chillies with the heat bred down; they are chillies with the last enzyme in the heat pathway switched off, an allele the authors note has been used in pepper breeding for a very long time.

The practical consequences are that bell peppers carry essentially no capsaicin, so they do not irritate the stomach or oesophagus the way chillies can in people with reflux or gastritis, are safe for young children and people with mouth ulcers, and — as the blood sugar and weight article explains — do not have the modest metabolic effects attributed to capsaicin. Claims that bell peppers "boost metabolism" borrow evidence from a compound they do not contain.

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The Skin, Digestion and Sensitive Guts

The skin of a bell pepper is a thin cuticle of cutin and wax over a layer of thick-walled cells — the plant's waterproofing. Human digestion has no enzyme for cutin or for the cellulose in those walls, so the skin passes through largely intact, which is why translucent curls of pepper skin are a normal finding in the stool a day after a raw pepper salad and not a sign of poor digestion. Cooking softens the flesh but does little to the cuticle; roasting until the skin blisters lets it be peeled away, which is the traditional solution.

For most people this is harmless roughage. For some it is not:

• Irritable bowel syndrome and fructose malabsorption. The Monash University group whose work underpins the low-FODMAP diet (Varney and colleagues, 2017, on how the cut-off values are set) tests individual foods at serving sizes. Green bell pepper is a low-FODMAP food at a normal serving; ripe red and yellow peppers carry more sugar, and a large serving can supply enough fructose in excess of glucose to bother fructose-sensitive people. Their current app gives the serving-size cut-offs, which are updated as foods are retested. For an IBS sufferer, green peppers in moderate amounts are the safer starting point, and roasted, peeled pepper is gentler than raw.
• Gastroparesis, strictures, and recovery from diverticulitis or bowel surgery. Low-residue advice in these situations reasonably excludes raw pepper skin. Peeled, well-cooked pepper is usually acceptable; the fibre is in the skin and the seeds.
• Reflux. Raw peppers are a commonly reported trigger for some people, probably through bulk and slow gastric emptying rather than any irritant, since there is no capsaicin. Cooked pepper is often tolerated when raw is not.

The seeds and the white pith are edible and harmless; they are simply bitter and fibrous, which is why recipes remove them.

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Other Practical Cautions

• Warfarin and vitamin K. Bell peppers are a trivial vitamin K source — USDA lists 4.9 micrograms per 100 g for red and 7.4 for green, against several hundred for a serving of kale — so they do not need to be counted by people on warfarin.
• Kidney disease and potassium. At 175 to 212 mg per 100 g, peppers are among the lower-potassium vegetables and are usually permitted on potassium-restricted diets; the renal dietitian's list is the authority.
• Latex-fruit syndrome. People with latex allergy can cross-react to several plant foods (banana, avocado, kiwi, chestnut most often); bell pepper has been reported occasionally among them. Anyone with latex allergy who reacts to peppers should mention both to their allergist.
• Choking. Raw pepper is firm and slippery; for toddlers, cut it into thin strips rather than rounds, or cook it soft.
• Food safety. Peppers have been implicated in produce-borne outbreaks like any raw vegetable. Rinse before cutting, refrigerate cut pepper, and use it within a few days.

None of these is a reason for a healthy person to eat fewer peppers. Taken together, the safety picture is that of a vegetable with one common, mild, cook-away allergy, no toxin of consequence, and a residue exposure far below any threshold — which is about the best a food can do.

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Key Research Papers

Author names, titles and journals are plain text; only the PMID or DOI is a link. Every identifier below was checked against PubMed or Crossref before publication.

1. Tedeschi SK, Frits M, Cui J, et al. (2017). Diet and rheumatoid arthritis symptoms: survey results from a rheumatoid arthritis registry. Arthritis Care & Research. — PubMed PMID: 28217907
2. England BR, Smith BJ, Baker NA, et al. (2023). 2022 American College of Rheumatology guideline for exercise, rehabilitation, diet, and additional integrative interventions for rheumatoid arthritis. Arthritis Care & Research. — PubMed PMID: 37227116
3. Skoczyńska M, Świerkot J (2018). The role of diet in rheumatoid arthritis. Reumatologia. — PubMed PMID: 30237632
4. Friedman M (2006). Potato glycoalkaloids and metabolites: roles in the plant and in the diet. Journal of Agricultural and Food Chemistry. — PubMed PMID: 17090106
5. Price A, Ramachandran S, Smith GP, Stevenson ML, Pomeranz MK, Cohen DE (2015). Oral allergy syndrome (pollen-food allergy syndrome). Dermatitis. — PubMed PMID: 25757079
6. Jensen-Jarolim E, Santner B, Leitner A, et al. (1998). Bell peppers (Capsicum annuum) express allergens (profilin, pathogenesis-related protein P23 and Bet v 1) depending on the horticultural strain. International Archives of Allergy and Immunology. — PubMed PMID: 9652302
7. Willerroider M, Fuchs H, Ballmer-Weber BK, et al. (2003). Cloning and molecular and immunological characterisation of two new food allergens, Cap a 2 and Lyc e 1, profilins from bell pepper (Capsicum annuum) and tomato (Lycopersicon esculentum). International Archives of Allergy and Immunology. — PubMed PMID: 12915767
8. Ebner C, Hirschwehr R, Bauer L, et al. (1995). Identification of allergens in fruits and vegetables: IgE cross-reactivities with the important birch pollen allergens Bet v 1 and Bet v 2 (birch profilin). Journal of Allergy and Clinical Immunology. — PubMed PMID: 7751517
9. Leitner A, Jensen-Jarolim E, Grimm R, et al. (1998). Allergens in pepper and paprika. Immunologic investigation of the celery-birch-mugwort-spice syndrome. Allergy. — PubMed PMID: 9491227
10. Vermeulen AM, Groenewoud GC, de Jong NW, et al. (2003). Primary sensitization to sweet bell pepper pollen in greenhouse workers with occupational allergy. Clinical and Experimental Allergy. — PubMed PMID: 14519152
11. Winter CK, Katz JM (2011). Dietary exposure to pesticide residues from commodities alleged to contain the highest contamination levels. Journal of Toxicology. — PubMed PMID: 21776262
12. Krol WJ, Arsenault TL, Pylypiw HM Jr, Incorvia Mattina MJ (2000). Reduction of pesticide residues on produce by rinsing. Journal of Agricultural and Food Chemistry. — PubMed PMID: 11052716
13. Yang T, Doherty J, Zhao B, Kinchla AJ, Clark JM, He L (2017). Effectiveness of commercial and homemade washing agents in removing pesticide residues on and in apples. Journal of Agricultural and Food Chemistry. — PubMed PMID: 29067814
14. Bradman A, Quirós-Alcalá L, Castorina R, et al. (2015). Effect of organic diet intervention on pesticide exposures in young children living in low-income urban and agricultural communities. Environmental Health Perspectives. — PubMed PMID: 25861095
15. Stewart C Jr, Kang BC, Liu K, et al. (2005). The Pun1 gene for pungency in pepper encodes a putative acyltransferase. The Plant Journal. — PubMed PMID: 15918882
16. Varney J, Barrett J, Scarlata K, Catsos P, Gibson PR, Muir JG (2017). FODMAPs: food composition, defining cutoff values and international application. Journal of Gastroenterology and Hepatology. — PubMed PMID: 28244665

PubMed Topic Searches

1. PubMed: nightshade vegetables and arthritis (note how little there is)
2. PubMed: bell pepper allergy and profilin
3. PubMed: removing pesticide residues from produce by washing

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Connections

• All Food
• Bell Peppers
• Bell Pepper Benefits: What the Evidence Actually Shows
• Bell Peppers: Nutrient Profile
• Bell Pepper Vitamin C: Red Versus Green
• Bell Pepper Carotenoids, Capsanthin, and Eye Health
• Bell Peppers, Blood Sugar, Weight, and the Heart
• Rheumatoid Arthritis
• Arthritis
• Irritable Bowel Syndrome
• Tomatoes
• Toxins

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