Nightshades: tomatoes, potatoes, peppers — and what the evidence really supports

This page covers the nightshade family — tomatoes, potatoes, peppers, chilli, paprika and aubergine — and what is genuinely known about them. It explains what glycoalkaloids are, why the “nightshades cause inflammation” idea is far more popular online than it is supported by evidence, where nightshades hide in spice blends and sauces, and how to run a fair six-week elimination if you want to test the idea on yourself rather than take it on trust. Our £49 Gold hair sample screen covers 700+ items (350 foods and 350 non-food items) and gives you a shortlist worth exploring first instead of a blank page and a guess. Results come within 3 working days of your sample arriving at our UK lab.

What this screen is — and what it is not

What it is

• A hair sample screen across 700+ items on the Gold panel, including tomato, potato, sweet pepper, chilli, paprika and aubergine, which returns a list of entries generated by the proprietary, non-diagnostic process
• A way to structure an elimination diet: a short, ordered shortlist worth exploring first, rather than cutting out everything at once and learning nothing
• Simple to send: 9–10 strands of hair, posted by you (we do not supply a kit), analysed at a UK lab, with results in 3 working days from arrival — allow 5–7 days from posting
• Available for anyone aged 6 and over, with sample data retained for 6 months
• Covered by a 90-day money-back guarantee, on the conditions that you follow the plan for 6 weeks and keep a food diary

What it is not

• Not a diagnostic test. Hair screening has no proven accuracy, and the report on its own proves nothing about your body. The useful evidence comes from your own elimination and reintroduction, written down
• Not a measurement of glycoalkaloids, lectins or anything else in the food, and not a measurement of anything in your blood or gut
• Not an allergy test. Allergy is an immune reaction and is assessed by the NHS, not by us
• Not a test for arthritis, eczema, psoriasis or any other named condition. We do not screen for these and cannot say anything about them — joint, skin or bowel symptoms belong with your GP
• Not a treatment, cure or fix. Nothing about reading a report changes how you feel; only the dietary changes you choose to trial can do that

Which foods are actually nightshades

Nightshades are plants in the Solanaceae family. The edible ones most people in the UK eat every week are tomatoes, potatoes, aubergine, sweet peppers and all the chillies — which means paprika, cayenne, chilli powder and pimento too, because those are simply dried, ground peppers. Several foods get wrongly swept into the list, which matters, because an elimination diet that cuts foods unnecessarily is harder to stick to and tells you less.

Glycoalkaloids: what is actually established

Glycoalkaloids are natural compounds that nightshade plants produce as a defence against insects and fungi. Potatoes make solanine and chaconine; tomatoes make tomatine; aubergine makes solasonine and solamargine. These are real compounds with real effects at high enough doses, and that is where the honest account has to stop — the dose is the whole argument.

Green and sprouted potatoes

The one well-documented, non-controversial nightshade problem is glycoalkaloid content in potatoes that have gone green or started sprouting. Solanine concentrates in the skin, in the green areas and in the sprouts, and it rises when potatoes are stored in light or warmth. At high intakes it causes acute gastrointestinal upset — nausea, vomiting, stomach cramps — and cases of this are documented in the medical literature. The practical advice is the same as standard food-safety guidance: store potatoes somewhere cool and dark, cut away green patches and sprouts generously, and throw away potatoes that taste bitter. Cooking does not reliably destroy solanine; peeling and discarding the green parts is what reduces it.

Tomatine and the rest

Tomatine is highest in green, unripe tomatoes and falls as the fruit ripens. At the levels found in ordinary ripe tomatoes there is no established human harm. The same applies to aubergine glycoalkaloids at normal culinary portions. In other words, the compounds that get named in nightshade articles are genuine, but the leap from “this plant contains a defence compound” to “this plant is harming you at dinner” is a leap, not a finding.

Nicotine and lectins

Two other claims circulate. Nightshades do contain nicotine, but in traces so small that dietary exposure is negligible next to tobacco — this is not a meaningful reason to avoid tomatoes. Lectins are also cited, usually on the basis of laboratory work or data on raw and undercooked plants; ordinary cooking substantially reduces lectin activity, and the case that dietary lectins from cooked nightshades cause harm in healthy people is not established.

The nightshade inflammation claim, honestly

The claim that nightshades drive inflammation is everywhere online. The evidence behind it is thin, and we would rather say that plainly than sell you a screen on a premise we cannot defend.

The modern version of the idea traces largely to a hypothesis put forward decades ago by a horticulturalist, supported by surveys of self-selected volunteers who already believed nightshades affected them. That is not a controlled trial, and it is not blinded. There is no good body of randomised human evidence showing that removing nightshades reduces inflammation in the general population. If you search NHS, dietetic or rheumatology guidance, you will not find nightshade avoidance recommended, and you should weigh that absence heavily.

Why does it so often seem to work anyway? Several unglamorous reasons. Cutting nightshades removes a large slice of processed food at the same time — ready meals, takeaways, crisps, sauces, spiced snacks — so people frequently change far more than tomatoes. Symptoms fluctuate on their own and tend to be recorded when they are at their worst, so the next few weeks often look better regardless. And when you expect a change, you notice the days that fit. None of this means your experience is imaginary; it means an uncontrolled experiment cannot tell you which change did the work.

There are also genuine, specific reactions that get mislabelled as a nightshade problem. Capsaicin, the heat compound in chilli, is a direct irritant and can plausibly trigger reflux, burning or urgency in some people — that is about chilli, not about the botanical family. Tomatoes are acidic and are a common self-reported reflux trigger. And true allergy to tomato or potato exists, though it is uncommon; allergy causes immediate immune symptoms such as hives, swelling or breathing difficulty, needs urgent medical attention, and is not what our screen looks at.

Does this sound like you?

• Discomfort after tomato-based meals — pasta sauce, pizza, curry, baked beans — but not after plain versions of the same dishes
• Burning, reflux or urgency specifically after spicy food, while mild tomato dishes seem fine
• Symptoms after takeaways and ready meals that you cannot reproduce when you cook the same thing from scratch
• You have already tried cutting “nightshades” informally, felt better for a while, then lost track of what you were actually avoiding
• Reactions to crisps, spice rubs, jerk or Cajun seasoning, chorizo or pepperoni that seem out of proportion to a small portion
• You cannot tell whether it is the tomato, the chilli, the onion and garlic, the wheat or the sheer size of the meal — because you have never tested them separately

Where nightshades hide

This is the part people underestimate. Whole tomatoes and chips are easy to spot; ground peppers are not. Paprika and cayenne appear in an enormous range of savoury products, sometimes declared only as “spices” or “natural flavouring”, and potato starch is a routine thickener and binder. A nightshade elimination that only removes the obvious foods is not really a test of anything.

What our screen can and cannot do here

Our report will show which entries were generated by the proprietary, non-diagnostic process, and nightshades are well represented on the panel — tomato, potato, sweet pepper, chilli, paprika and aubergine are all covered on the Gold list, alongside the sauces and blends they hide in. What the report cannot do is prove that any of those foods affect you. Hair screening has no proven accuracy for identifying food intolerance, and we are not going to pretend otherwise.

What it is useful for is structure. Most people who suspect nightshades never actually test the idea: they cut tomatoes for ten days, eat a paprika-heavy sausage without noticing, feel no clearer, and give up. A written shortlist turns an open-ended worry into a defined experiment with a beginning and an end. If you would run the elimination properly either way, the screen is optional. If a written starting point is what gets you to run it at all, that is what you are paying for — and if it does not help, the 90-day money-back guarantee applies when you have followed the plan for six weeks with a food diary.

How to run a focused six-week elimination

Speak to your GP before making significant dietary changes, particularly for a child, in pregnancy, or if you have ongoing symptoms that have not been assessed. A registered dietitian can keep the diet from becoming narrower than it needs to be.

1. Before you start. Spend a week recording what you eat and how you feel, without changing anything. Without a baseline you cannot judge the change. Note portion size, alcohol, sleep and stress alongside the food — all of them affect digestive symptoms.
2. Weeks 1–2: remove all nightshades properly. That means tomato, potato, peppers, chilli, paprika and aubergine in every form, including spice blends, sauces, crisps, processed meats and potato starch. Cook from scratch. Replace the flavour with fresh herbs, black pepper, cumin, coriander, turmeric, lemon and vinegar. Use sweet potato, parsnip, celeriac or rice in place of potato.
3. Weeks 3–4: hold steady and keep writing. Score your main symptoms out of ten each day rather than writing “bad day”. Numbers make a pattern visible that adjectives hide. If nothing has shifted at all by the end of week four, that is a real result — nightshades are probably not your issue, and it is worth going back to your GP rather than cutting more foods.
4. Weeks 5–6: complete the phase. Finish even if you feel better early. A stable baseline is what makes reintroduction readable, and six weeks with a diary is also the condition attached to the guarantee.
5. Reintroduce one food at a time, in order. Leave 4–5 days between trials. A sensible order is: peeled cooked potato first, then cooked tomato, then raw tomato, then sweet peppers, then aubergine, and chilli or paprika last, since capsaicin is a separate irritant that can confuse the picture. Eat a normal-sized portion, not a token amount, and watch for 48 hours.
6. Confirm before you conclude. If a food seems to cause symptoms, wait a week and test it once more. One bad day is not a pattern. If it repeats, you have found something specific and worth respecting — and it will usually be one or two foods, not the whole family.
7. Rebuild the diet. Bring back everything that passed. Long-term avoidance of foods that never actually caused a problem costs you nutrition, money and enjoyment for nothing. Potatoes are a meaningful source of potassium and vitamin C in the UK diet, and peppers and tomatoes contribute vitamin C too.

Common questions

Is nightshade intolerance a recognised medical condition?

No. There is no recognised diagnosis of nightshade intolerance, no validated test for it, and no NHS or dietetic guidance recommending nightshade avoidance. Individual people can and do react to individual nightshade foods — chilli and tomato in particular — but that is a specific food response, not a family-wide condition. We would rather tell you that than imply a diagnosis exists.

I have read that nightshades make joint pain worse. Should I cut them out?

The claim is popular but poorly evidenced, and controlled human trials supporting it do not exist. Our screen does not test for arthritis or any other named condition and can tell you nothing about it, so please take joint symptoms to your GP for proper assessment. If you still want to test the idea for yourself, run the six-week elimination above with a diary so you get an answer rather than an impression — and reintroduce afterwards rather than avoiding indefinitely on a hunch.

Are green potatoes genuinely a problem?

Yes, and this is the one nightshade issue that is not in dispute. Green patches and sprouts carry much higher glycoalkaloid levels, and at high intakes these cause acute stomach upset. Store potatoes cool and dark, cut green areas and sprouts away generously, and discard any potato that tastes bitter. This is ordinary food safety and applies to everyone, whether or not you think nightshades affect you.

Does cooking remove glycoalkaloids?

Not reliably. Solanine is fairly heat-stable, so boiling, roasting or frying does not remove it in the way cooking reduces some other plant compounds. Peeling and cutting away green or sprouted parts is what lowers it. For ripe tomatoes and normal portions of aubergine the question is largely academic, because the levels involved are low to begin with.

Why might paprika bother me when fresh peppers do not?

Dried ground spices are concentrated, and they turn up in far more meals than you would guess — often several times a day across sauces, snacks and processed meat. Chilli-based spices also carry capsaicin, a direct irritant with effects that fresh sweet peppers do not have. If your report flags paprika or chilli but not sweet pepper, that is worth taking seriously as a reason to test them separately during reintroduction.

Will the screen tell me whether I am intolerant to nightshades?

No. It gives you a list of entries generated by the proprietary, non-diagnostic process, which may help you spot patterns and decide what to trial first. It cannot confirm that any food affects you, and it is not a diagnostic test. If you want proof, the elimination and reintroduction is the proof — the report is just the running order.

Which package covers nightshades?

All of them include the main nightshade foods. Silver at £37 covers the top 100 items, Gold at £49 covers 700+ items including the sauces, blends and processed products where nightshades hide, and Platinum at £65 extends the panel further. There are also Couples at £74 and Family at £125, and a Personalised Meal Plan add-on at £10 if you would like the elimination weeks planned out for you.

Related reading

• How hair sample screening works — and what it cannot show
• Food intolerance versus food allergy
• Histamine and fermented or aged foods
• Garlic and onion, and hidden FODMAPs in sauces
• Stomach pain and cramps after eating

More: Food Intolerances A–Z