A bell pepper has no heat at all. The hottest chili peppers are rated in the millions of Scoville units, a scale devised in 1912 by an American pharmacist, Wilbur Scoville. Lab tests of the heat compounds gave about 34,000 units for a serrano, 247,000 for a habanero and 665,000 for a Bhut jolokia. Pure capsaicin, the main heat compound, is listed at 16 million.
The heat is a defense aimed at mammals. Capsaicin discourages the animals that eat the fruit without deterring the ones that spread its seeds, and birds are indifferent to its burn.
Researchers traced the difference to the receptor that senses capsaicin. A single domain, a section of the receptor, makes the rat version sensitive and the chicken version not. That receptor also responds to painful heat, which is why a chili feels hot and not just sharp.
A raw red chili is a small food. One pepper (45 g) has 18 calories, 72% of the Daily Value (the FDA’s daily target) for vitamin C and 13% for vitamin B6. Most of the research below is not on a pepper like that. It covers spicy food as a whole, chili powder in capsules, or capsaicin alone, and each card says which.
Health benefits of chili peppers
The top findings from 30 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★Signs of more fat burning in longer studiesA review of 24 randomized studies of red pepper and capsaicin found a lower respiratory quotient in longer studies, a sign of more fat burning. Energy use did not clearly change.
- ★★Slightly less food eaten at the next mealCapsaicinoids, the heat compounds of chili, taken before a meal cut intake by about 74 kcal across 8 trials. Results varied a lot between trials.
- ★★Only a small weight loss from capsaicin pillsCapsaicin supplements, not chili peppers, lowered weight by only 0.51 kg across 15 trials in overweight and obese adults. The authors call the effects modest.
- ★Mixed effects on stomach and gut symptomsRed pepper powder cut indigestion symptoms by about 60% in 15 people, against under 30% in 15 on placebo. In diarrhea-type IBS, chili caused more belly pain than in healthy people.
- ★No change in blood sugar or cholesterolIn 36 adults, 30 g a day of a chili blend for 4 weeks left blood sugar, cholesterol and blood pressure unchanged. That dose is far above a usual serving.
All 30 studies, strongest evidence first
Longer red pepper studies found signs of more fat burning
This review pooled 22 publications covering 24 randomized controlled studies of red pepper and capsaicin, including 24-hour respiratory chamber studies. In longer studies the respiratory quotient fell, a sign of more fat burning. Energy use did not clearly change in one-meal or long-term studies, and capsaicin also countered the drop in fullness during a calorie deficit. Appetite and intake results were mixed, and all four authors report ties to the McCormick Science Institute.
Capsaicinoids before a meal cut intake by about 74 kcal
This meta-analysis pooled 8 trials with 191 people, who took capsaicinoids (the heat compounds of chili) from chili or as capsaicin before a meal. Results varied a lot between trials (I2 of 75.7%). The authors suggest at least 2 mg of capsaicinoids is needed, with a shift toward carbohydrate-rich foods over fatty ones. They call for longer trials.
Capsaicin supplements lowered weight by only 0.51 kg across 15 trials
This meta-analysis pooled 15 randomized trials with 762 overweight and obese adults. Body mass index fell 0.25 kg/m² and waist size 1.12 cm. These were capsaicin supplements, not chili peppers, and the authors call the effects modest.
1 g red pepper raised energy use and core body temperature
In this randomized crossover trial, 25 healthy adults ate meals with 1 g of ground red pepper, their preferred amount, or none. The preferred amount was 1.8 g in 13 regular spicy food users and 0.3 g in 12 non-users. About 1 g a meal is what Americans prefer on average. Energy intake fell after 1 g only in non-users, which suggests people get used to the effect.
Chili at every meal raised fullness when people ate enough calories
In this randomized crossover trial, 15 people in a respiration chamber added 1 g of red chili pepper to every meal. Each meal held 2.56 mg of capsaicin (1.03 g of chili, 39,050 Scoville units). Intake at a free-choice dinner tended to fall, but the drop could be chance. On a calorie-cut day, capsaicin kept the desire to eat from rising after dinner.
The hottest bearable red pepper soup cut fat intake at that lunch
This randomized trial in 16 Japanese men compared placebo with a moderate and a strong dose of red pepper in soup. It also tested strong red pepper in capsules. The strong dose was the most each man could bear, far more than most people add to food. The moderate dose changed nothing, and capsules only tended to lower fat intake, so the mouth burn does not seem to be needed.
Four weeks of chili lowered the insulin rise after a chili meal
In this randomized crossover trial, 36 adults ate 30 g a day of a chili blend (55% cayenne) or a bland diet. Each lasted 4 weeks, and the chili dose was far more than a usual serving. Insulin rose least when a chili meal followed 4 weeks of chili. In people with a body mass index of 26.3 or above, C-peptide and energy use after the meal were also lowest.
Chili blend daily left blood sugar, cholesterol and blood pressure unchanged
This randomized crossover trial in 36 adults used the same far-above-usual dose: 30 g a day of a blend with 55% cayenne. It was compared with a bland diet over 4 weeks. Men had a lower resting heart rate on the chili diet. The authors saw no obvious benefit or harm in metabolism.
Chili powder raised gut Faecalibacterium and lowered the hunger hormone ghrelin
Over 6 weeks, 12 healthy adults in a controlled feeding trial had 0, 5, 0 and then 10 mg of capsaicin daily from chili powder. The gut hormones GLP-1 and GIP also rose. The effects were mostly in people with a Bacteroides gut type, and the study was small.
Daily chilli raised an acid reflux score from 7 to 13
In this study, 12 healthy people without reflux symptoms ate 3 g of cascabel or ancho chilli a day. They had 24-hour esophageal pH (acid) tests before and after. The increase was clear for cascabel (880 ppm capsaicin) but not for the milder ancho (488 ppm). The authors say the amount of reflux seems to depend on the type of chilli.
In diarrhea-type IBS, chili caused more belly pain than in healthy people
This crossover trial included 20 people with IBS-D (irritable bowel syndrome with diarrhea) and 38 healthy volunteers. They ate a standard meal, the meal mixed with 2 g of chili, or the meal with 2 g of chili in capsules. Belly pain and burning were greater in the IBS-D group, while healthy people felt only mild burning. Oral burning was the same in both groups, and colonic transit did not change.
Chili capsules caused more abdominal burning in non-erosive reflux disease
In this randomized crossover trial, 15 healthy volunteers and 15 patients with non-erosive reflux disease took 2 g of chili in capsules or a placebo. In patients, the stomach made more room after chili (451 against 375 mL with placebo), with less fullness and a trend toward more heartburn. Healthy volunteers had similar symptoms with chili and placebo.
Red pepper powder cut dyspepsia symptoms by about 60%, placebo under 30%
In this double-blind trial, 30 patients with functional dyspepsia (ongoing indigestion) took red pepper powder before meals (15) or a placebo (15). The dose was 2.5 g a day for 5 weeks. Pain, fullness and nausea scores were lower from week 3. The authors suggest capsaicin desensitizes stomach pain fibers; the trial was small.
Chili capsules before meals reduced belly burning after eating in IBS-D
In this randomized crossover trial, 16 patients with diarrhea-type IBS took chili or placebo capsules 3 times a day for six weeks. There was a 4-week washout between them. The first rectal sensation moved from 8 to 16 mmHg, which hints that the gut became less sensitive. Other symptoms did not change.
A capsaicin supplement lowered blood sugar after meals in gestational diabetes
In this placebo-controlled trial, 44 pregnant women with gestational diabetes, at 22 to 33 weeks, took a chili supplement for 4 weeks. It gave 5 mg of capsaicin a day, and 42 women finished. Two-hour blood sugar and insulin, and fasting cholesterol and triglycerides, fell, and fewer babies were large for gestational age. The trial was small and tested a set capsaicin dose, not a chili meal.
Spicy food 6 or 7 days weekly: 14% lower risk of dying
The China Kadoorie Biobank followed 199,293 Chinese men and 288,082 women for a median 7.2 years, and 11,820 men and 8,404 women died. The comparison was with people who ate spicy food less than once a week. Lower risks were also seen for deaths from cancer, ischemic heart disease and respiratory disease. Spicy foods in general were counted, not chili alone, and eating habits were reported once.
Chili more than 4 times weekly: 23% lower risk of dying
The Moli-sani cohort followed 22,811 Italian adults for a median 8.2 years, with 1,236 deaths. The comparison was with people who rarely ate chili. Deaths from heart and blood vessel disease were also lower (0.66 times the risk). Known blood markers explained little of the link, and it held regardless of how closely people followed a Mediterranean diet.
US hot red chili eaters had a 13% lower risk of dying
The NHANES III survey (a US national health survey) followed 16,179 adults for a median 18.9 years, with 4,946 deaths. Of those who ate hot red chili peppers, 21.6% died, against 33.6% of those who did not (0.87 times the risk after adjustment). Trends for deaths from vascular disease were similar but could be chance.
Pooled cohorts: regular chili eaters had a 12% lower risk of dying
This meta-analysis pooled 4 cohorts from the United States, China, Italy and Iran, with 564,748 adults followed a median 9.7 years. Deaths from heart disease were lower (0.82 times the risk), but deaths from cerebrovascular disease (stroke) were not clearly lower. Chili pepper, chili sauce and chili oil were all counted.
Spicy food went with 3 to 5% lower vascular disease risk
The China Kadoorie Biobank followed 486,335 Chinese adults for a median 12.1 years, with 136,125 cases of vascular disease. Risk was lowest at 1 to 2 days a week (0.95 times the risk), and the benefit did not grow with more days. The link held for ischemic heart disease and major coronary events.
Spicy food at least once a week: 6% lower cardiovascular risk
The China Kadoorie Biobank followed 26,163 Chinese people with diabetes and no heart disease or stroke for a median 8.5 years. Major cardiovascular events occurred in 18.6% of the 8,837 who ate spicy food and 22% of the 17,326 who did not. That is 0.94 times the risk, a borderline result.
An umbrella review found the health effect of spicy food unclear
This umbrella review (a review of reviews) covered 11 systematic reviews and meta-analyses of spicy food and chili peppers, with 27 findings. Lower mortality, cardiovascular disease and metabolic problems sat on one side. Higher esophageal, gastric and gallbladder cancer sat on the other. The authors call spicy food typically safe but say high-quality proof is lacking.
High chili intake went with 2.7 times the odds of esophageal cancer
This meta-analysis pooled 14 case-control studies (which compare people with and without a disease), with 5,009 gastrointestinal cancers among 11,310 people. Overall the odds were 1.64 times as high, a borderline result, with no clear link for stomach or colorectal cancer. Odds were higher in Asian, African and North American studies, and lower in South American and European ones. Case-control studies depend on recall.
In Chile, gallbladder cancer was linked to heavy red chili eating
This case-control study compared 114 gallbladder cancer patients with 114 matched hospital patients with gallstones. After adjustment, high intake had about 3 times the odds (3.2), and very low income was another independent factor (6.3). A lab study below found aflatoxin in some red chili peppers from Bolivia and Peru.
More than 50 g of chili daily: lower thinking test scores
This open cohort from the China Health and Nutrition Survey followed 3,302 adults for 15 years. They took cognitive tests at least twice, and chili intake came from 3-day food records. Compared with non-eaters, heavy eaters had higher odds of self-reported poor memory (2.12) and memory decline (1.56). The link was stronger in people with a low body mass index.
Daily spicy eaters had a higher body mass index
The China Kadoorie Biobank included 434,556 Chinese adults. Those who ate spicy food every day had a body mass index (weight for height) higher by 0.44 in men and 0.51 in women. Body fat, waist size and waist-to-height ratio also rose with how often, how strongly and for how long people ate spicy food. The authors call spicy food a risk factor for obesity and say the reason is unclear.
Lab tests of 15 chillies rated Bhut jolokia at 665,000 Scoville units
This lab study measured the four main heat compounds in chillies grown in Denmark and converted them to Scoville units. Serrano came out at 34,000 units and habanero at 247,000. The figures matched earlier ones from traditional growing areas. Capsaicin made up 31% to 71% of the heat compounds, depending on the variety.
Roasting or frying green chilies left no detectable vitamin C
In this lab test of one batch of green chilies, cooking cut the heat compounds. They stayed higher after roasting (730 mg/kg) than after frying (502.56 mg/kg), and vitamin A was gone after frying. The raw chilies carried aflatoxins (mold toxins) above EU limits for spices. Frying brought all four below the limits, but roasting did not for the main one, B1.
Some Bolivian and Peruvian red chilies contained aflatoxin B1
This lab test covered 7 samples (3 from Bolivia, 4 from Peru) and 3 controls (2 from China, 1 from Japan). Aflatoxin, a mold toxin, turned up in some but not all of the Bolivian and Peruvian samples. One sample was above the European Commission’s proposed limit for spices. The authors raise a possible link to the high gallbladder cancer rates there and ask for a case-control study to check it.
Mice fed capsaicin had less brain amyloid and fewer memory problems
This study was in mice bred to develop Alzheimer’s-type disease, not people. It tested capsaicin, the heat compound of chili peppers, not chili itself. The authors say clinical trials are needed. The study in people above found the opposite pattern in heavy chili eaters.
Who should be careful with chili peppers
Most people can eat chili peppers freely. Take a little care if one of these applies:
- Heartburn and reflux. The NHS (the UK health service) lists spicy food among the things that can cause or worsen heartburn. It advises skipping foods that trigger your symptoms. In a small trial, 2 g of chili in capsules caused more abdominal burning in people with non-erosive reflux disease.
- Irritable bowel syndrome. In a trial of people with diarrhea-predominant IBS, a meal with 2 g of chili caused more belly pain and burning than in healthy people. Monash lists one red chilli (28 g) as an optional ingredient in a low-FODMAP stir-fry recipe. If chili bothers you, leave it out.
- Very hot peppers and bare hands. Doctors have reported a ruptured esophagus after violent vomiting at a ghost pepper eating contest. They also reported a thunderclap headache after a Carolina Reaper. These are rare cases tied to ultra-hot peppers, not ordinary chili. Wear gloves or wash your hands well after cutting hot peppers, and keep them away from your eyes.
How to choose, store and eat chili peppers
- Fresh: one raw red chili (45 g) has 18 calories and 72% of the Daily Value for vitamin C. But roasting or frying green chilies left no detectable vitamin C in a lab test.
- Heat: lab tests gave about 34,000 Scoville units for a serrano, 247,000 for a habanero and 665,000 for a Bhut jolokia. A bell pepper has none.
- Powder and flakes: trials used about 1 g of red pepper a meal, near what Americans prefer on average. A dyspepsia trial used 2.5 g a day. The 30 g a day in one trial is far more than a usual serving.
Pick full-sized, firm peppers with no wrinkling and the stem still attached. Keep them in the vegetable drawer of the fridge, where they are best within one to two weeks.
Residues are no reason to skip them. In USDA tests of 651 samples of fresh jalapeño, Anaheim and serrano peppers in 2019, 2 samples had a residue above the legal limit.
Sources
- Heartburn and acid reflux. NHS.
- Patcharatrakul T, Kriengkirakul C, Chaiwatanarat T, Gonlachanvit S. Acute effects of red chili, a natural capsaicin receptor agonist, on gastric accommodation and upper gastrointestinal symptoms in healthy volunteers and gastroesophageal reflux disease patients. Nutrients. 2020.
- Gonlachanvit S, Mahayosnond A, Kullavanijaya P. Effects of chili on postprandial gastrointestinal symptoms in diarrhoea predominant irritable bowel syndrome: evidence for capsaicin-sensitive visceral nociception hypersensitivity. Neurogastroenterol Motil. 2009.
- Low FODMAP vegetable stir fry recipe. Monash FODMAP.
- Arens A, Ben-Youssef L, Hayashi S, Smollin C. Esophageal rupture after ghost pepper ingestion. J Emerg Med. 2016.
- Boddhula SK, Boddhula S, Gunasekaran K, Bischof E. An unusual cause of thunderclap headache after eating the hottest pepper in the world: “The Carolina Reaper”. BMJ Case Rep. 2018.
- Taylor CS, Kelly BM, Nichols TA. Fear the reaper: reversible cerebrovascular vasoconstriction syndrome after hot pepper ingestion. Radiol Case Rep. 2020.
- Colorado peppers. Colorado State University Extension.
- Pesticide Data Program annual summary, calendar year 2019. USDA Agricultural Marketing Service.
- Duelund L, Mouritsen OG. Contents of capsaicinoids in chillies grown in Denmark. Food Chem. 2017.
- Bashir O, Sharma V, Hussain SZ, et al. Effect of roasting and frying treatments on aflatoxins and capsaicinoids content and nutritional profile of green chilies (Capsicum annum L.). Food Sci Nutr. 2022.
- Ludy MJ, Mattes RD. The effects of hedonically acceptable red pepper doses on thermogenesis and appetite. Physiol Behav. 2011.
- Bortolotti M, Coccia G, Grossi G, Miglioli M. The treatment of functional dyspepsia with red pepper. Aliment Pharmacol Ther. 2002.
- Ahuja KD, Robertson IK, Geraghty DP, Ball MJ. Effects of chili consumption on postprandial glucose, insulin, and energy metabolism. Am J Clin Nutr. 2006.
History of chili peppers
Chili peppers are American plants. Genetic, language and plant-remains evidence points to the domestication of Capsicum annuum in Mexico. Preceramic remains (from before pottery) were found in the Valley of Tehuacán.
A 2024 study argues the process was spread over time and place, with at least two separate events. Lowland regions such as the Yucatán Peninsula and southern coastal Guerrero suited early meetings of people and wild chilies.
People ate them a very long time ago. Starch grains from chili peppers turn up at seven sites from the Bahamas to southern Peru. They date from about 6,000 years ago up to European contact. They appear alongside maize, which shows the two formed an ancient and widespread plant food pair, in some regions before pottery.
The name is mixed up twice. The word “chili” comes from the Nahuatl word chīlli and has nothing to do with the country Chile. The word “pepper” came from Columbus and his crew, who named the fruits after black pepper because they were pungent too.
In 1493 Diego Álvarez Chanca sailed with Columbus on his second voyage. In 1494 he published what he saw of their medicinal uses.
Chilies crossed the world fast. By the mid-1500s they were a common garden plant in Spain. They reached Italy by 1526, Germany by 1543 and the Balkans by 1569, where they were ground into paprika.
Portuguese and Spanish traders likely carried them to Africa and Asia in the 16th century, and Spanish ships took them to the Philippines. The earliest known Chinese record dates from 1591.
Heat got a number in 1912. Wilbur Scoville had a panel of five trained tasters sip diluted pepper extract until at least three could no longer detect heat. The dilution gave the rating. That test can vary by up to 50% between labs, so since the 1980s labs have measured the heat compounds directly with liquid chromatography.
Sources
- Kraft KH, Brown CH, Nabhan GP, et al. Multiple lines of evidence for the origin of domesticated chili pepper, Capsicum annuum, in Mexico. Proc Natl Acad Sci U S A. 2014.
- Chiou KL, Lira-Noriega A, Gallaga E, Hastorf CA, Aguilar-Meléndez A. Interdisciplinary insights into the cultural and chronological context of chili pepper (Capsicum annuum var. annuum L.) domestication in Mexico. Proc Natl Acad Sci U S A. 2024.
- Perry L, Dickau R, Zarrillo S, et al. Starch fossils and the domestication and dispersal of chili peppers (Capsicum spp. L.) in the Americas. Science. 2007.
- Tewksbury JJ, Nabhan GP. Seed dispersal. Directed deterrence by capsaicin in chilies. Nature. 2001.
- Jordt SE, Julius D. Molecular basis for species-specific sensitivity to “hot” chili peppers. Cell. 2002.
- Duelund L, Mouritsen OG. Contents of capsaicinoids in chillies grown in Denmark. Food Chem. 2017.
- Chili pepper. Wikipedia.
- Scoville scale. Wikipedia.
Frequently asked questions about chili peppers
Are chili peppers good for you?
Probably, in ordinary amounts, but the evidence is mostly observational and none of the 30 studies here reaches strong evidence. A raw red chili (45 g) has 18 calories and 72% of the Daily Value for vitamin C. A pooled analysis of 4 cohorts linked regular chili eating to a 12% lower risk of dying. That is a link, not proof, and other studies tie heavy intake to higher odds of esophageal cancer and lower scores on thinking tests.
Do chili peppers help you lose weight?
Only a little, and mostly in studies of capsaicin. A meta-analysis of 15 trials found capsaicin supplements lowered body weight by only 0.51 kg. Across 8 trials, capsaicinoids taken before a meal cut the energy eaten at that meal by about 74 kcal. In 434,556 Chinese adults, daily spicy eaters had a higher body mass index, not a lower one. One raw chili has 18 calories, so it adds flavor cheaply.
Do chili peppers cause heartburn or ulcers?
They can trigger heartburn in some people, and no study here tested ulcers. The NHS lists spicy food among heartburn triggers, and 2 g of chili in capsules caused more abdominal burning in reflux patients, not healthy volunteers. In a small trial of 30 patients with functional dyspepsia, 2.5 g of red pepper powder a day cut symptoms by about 60%. So people respond differently.
Do chili peppers cause cancer?
The evidence is mixed and comes from case-control studies, which cannot show cause. A meta-analysis of 14 of them linked high chili intake to about 2.7 times the odds of esophageal cancer. It found no clear link for stomach or colorectal cancer. In Chile, people with gallbladder cancer had about 3 times the odds of eating a lot of red chili. Large Chinese cohorts found fewer cancer deaths among spicy food eaters. A lab study found aflatoxin in some red chili peppers from Bolivia and Peru, which may be part of the story.
How much vitamin C is in a chili pepper?
One raw red chili (45 g) has 64.7 mg of vitamin C, which is 72% of the Daily Value. Gram for gram, only 2 of 99 foods in our database have more. Heat can remove it: roasting or frying green chilies left no detectable vitamin C in a lab test. So raw chili keeps the most.
How much chili can you eat a day?
No study here sets a safe or ideal amount. Trials used about 1 g of red pepper a meal and 2.5 g a day for dyspepsia. Another used 30 g a day of a chili blend for 4 weeks, and it did not change blood sugar, cholesterol or blood pressure. In the large Chinese cohort, risk was lowest with spicy food 1 to 2 days a week and did not fall further with more days. If heat or stomach symptoms bother you, that is your limit.
Why can’t birds feel chili heat?
Their version of the capsaicin receptor does not respond to it. Researchers found a domain of the rat receptor that makes it sensitive to capsaicin and the chicken receptor indifferent. The pepper gains from that, because capsaicin discourages the animals that eat the fruit without deterring the ones that spread its seeds.
Is chili powder as healthy as fresh chili?
It is a different food, and the numbers on this page are for raw red chili peppers. Powder is dried and used by the pinch, so trials gave about 1 g a meal or 2.5 g a day. No study here compares powder with fresh peppers. Cooking removed the vitamin C from green chilies in one lab test, so the two are not interchangeable.