For most people, nothing is wrong with tomatoes. They’re one of the most widely consumed fruits in the world, packed with vitamins, antioxidants, and fiber. But tomatoes do contain a handful of compounds that cause real problems for specific groups of people, and a few popular claims about their dangers deserve a closer look. Here’s what the evidence actually shows.
The Nightshade Problem
Tomatoes belong to the nightshade family (along with potatoes, peppers, and eggplant), and this is where most of the suspicion comes from. The concern centers on a group of compounds called glycoalkaloids, which plants produce as a natural defense against insects and disease. In tomatoes, the main one is called tomatine.
Green, unripe tomatoes have the highest concentrations of tomatine, with levels estimated at several hundred milligrams per 100 grams of fresh weight in the peel alone. As a tomato ripens and turns red, tomatine is converted into a nontoxic compound. By the time a tomato is fully ripe, concentrations drop to roughly 1 mg per 100 grams. To reach the dose where harmful effects begin in humans (around 2 to 5 mg per kilogram of body weight), you’d need to eat an enormous quantity of green tomatoes in a single sitting, or roughly 1,500 kg of ripe tomatoes in a day.
That said, eating large amounts of unripe green tomatoes can cause vomiting and diarrhea. Tomatine is also considered less dangerous than the glycoalkaloids found in green potatoes, because it has a much weaker effect on the nervous system. The practical takeaway: ripe tomatoes pose essentially zero glycoalkaloid risk. Fried green tomatoes in normal portions are fine, but don’t eat unripe tomatoes by the pound.
Tomatoes and Joint Pain
One of the most persistent claims is that nightshades, including tomatoes, trigger arthritis flares. This idea has been circulating for decades, and plenty of people with rheumatoid arthritis or psoriatic arthritis swear their joints feel worse after eating them. The Arthritis Foundation acknowledges this lived experience but notes there is very little scientific evidence on either side.
Older mouse studies suggested that solanine (a related compound found in potatoes, not tomatoes) could damage the gut lining and worsen intestinal inflammation. But more recent mouse research found the opposite: certain nightshade foods actually reduced inflammation, improved gut barrier function, and lowered levels of harmful gut bacteria. And mouse studies, as a rule, rarely translate cleanly to humans.
No clinical trial has demonstrated that removing tomatoes from the diet improves arthritis symptoms in a measurable way. If you notice a consistent pattern where your joints flare after eating tomatoes, an elimination diet supervised by a dietitian can help you confirm or rule out a personal sensitivity. But there’s no biological reason for the average person with arthritis to avoid them.
Histamine Reactions
Tomatoes can trigger symptoms in people with histamine intolerance. They don’t just contain histamine on their own; they also appear to stimulate the release of histamine already stored in the body. For someone whose body struggles to break down histamine efficiently, this double effect can cause headaches, flushing, hives, nasal congestion, or digestive upset after eating tomatoes or tomato-based foods like pasta sauce and pizza.
This isn’t a true allergy, and it won’t show up on a standard allergy test. Histamine intolerance is a threshold issue. You might tolerate a few slices of fresh tomato but react to a large bowl of marinara, especially if you’ve also had aged cheese, wine, or other histamine-rich foods in the same meal. If you suspect this is your situation, keeping a food diary for a few weeks can help you identify your personal limit.
Kidney Stones and Oxalates
People prone to calcium oxalate kidney stones are often told to avoid tomatoes. This turns out to be mostly a myth. Research published in the journal Current Urology found that tomatoes actually contain a low concentration of oxalates. They’re also high in citric acid, which helps prevent stone formation by binding to calcium before it can form crystals in the kidneys.
In fact, tomato juice combined with lemon juice has been studied as a potential alternative to standard citrate therapy for stone prevention, thanks to its high citrate and magnesium content and low sodium. The evidence isn’t strong enough yet for formal dietary recommendations, but it suggests tomatoes are more helpful than harmful for most kidney stone patients.
Pesticide Residue
Tomatoes sometimes get lumped in with heavily sprayed produce, but they’re not as bad as their reputation suggests. In the Environmental Working Group’s 2025 analysis of 47 fruits and vegetables, tomatoes ranked 27th, placing them squarely in the middle. They did not make the “Dirty Dozen” list of the 12 most contaminated items. Spinach, potatoes, and several fruits ranked significantly worse.
If pesticide exposure concerns you, washing tomatoes under running water and rubbing the skin removes a meaningful amount of surface residue. Buying organic is another option, but conventional tomatoes are not in the high-risk category.
Digestive Sensitivity
Tomatoes are naturally acidic, with a pH between 4.0 and 4.5. For people with gastroesophageal reflux (GERD) or a sensitive stomach, this acidity can worsen heartburn or cause discomfort, especially in concentrated forms like tomato paste, ketchup, or canned sauce. Cooking tomatoes down concentrates their acid, which is why a bowl of tomato soup might bother you more than a fresh tomato on a salad.
This isn’t a sign that tomatoes are inherently damaging to the stomach lining. It’s a mechanical issue: acidic food relaxes the valve between your esophagus and stomach, letting acid splash upward. If reflux is your main concern, eating smaller portions of fresh tomato with other foods (rather than drinking tomato juice on an empty stomach) often makes a noticeable difference.
What Tomatoes Actually Offer
The compound that gives tomatoes their red color, lycopene, is one of the most studied antioxidants in the food supply. It’s linked to lower rates of heart disease and certain cancers in large population studies. Here’s the interesting part: cooking tomatoes dramatically increases the amount of lycopene your body can absorb. Cornell University research found that heating tomatoes boosted their beneficial lycopene content by 54 to 171 percent depending on cooking time, compared to raw tomatoes. The form of lycopene that the body absorbs most easily increased by up to 35 percent with cooking.
Heating does reduce vitamin C content, so raw and cooked tomatoes each have trade-offs. Eating both gives you the broadest nutritional benefit. Adding a small amount of fat (olive oil, cheese, avocado) further improves lycopene absorption, since it’s a fat-soluble compound.
For the vast majority of people, tomatoes are not only safe but genuinely beneficial. The problems are real but narrow: histamine intolerance, acid reflux, and possible individual sensitivities in certain autoimmune conditions. If none of those apply to you, tomatoes are one of the better things you can eat.