Lemon

Lemon belongs to Rutaceae, the citrus or rue family. Kew’s Plants of the World Online (POWO) accepts the name Citrus × limon (L.) Osbeck, first published by Osbeck in his account of a voyage to the East Indies in 1765, and based on Linnaeus’s 1753 name Citrus medica var. limon, which treated the lemon as a variety of citron. POWO lists 84 synonyms, including Citrus limonum Risso and Citrus × limonia Osbeck, and many sources, including the FDA, still write Citrus limon (L.) Burm. f. The “×” marks a hybrid. POWO describes the lemon as a cultigen derived from artificial hybrids, gives its hybrid formula as C. maxima × C. medica × C. reticulata (pummelo, citron, and mandarin), and places it in the subtropical biome. Curk and colleagues (Annals of Botany 2016) analyzed 133 citrus accessions with nuclear and cytoplasmic markers and found that limes and lemons arose from many separate hybridizations; citron contributed to all of them and was the direct male parent of the yellow lemons, with sour (bitter) orange, C. aurantium, as the other parent. Where this first happened is uncertain: Julia Morton’s Fruits of Warm Climates (1987) calls the lemon’s true home unknown, though some have linked it to northwestern India.

Morton describes the true lemon as a tree 10 to 20 feet (3–6 m) tall, usually with sharp thorns on the twigs. The alternate leaves are reddish when young, then dark green above and paler beneath, oblong to elliptic, 6.25–11.25 cm long, finely toothed, with narrow wings on the leaf stalks. Mildly fragrant flowers open singly or in small clusters in the leaf axils from reddish buds, with four or five petals about 2 cm long that are white inside and purplish outside, and 20 to 40 stamens. The fruit is oval with a nipple-like tip, 7–12 cm long, with a light-yellow, aromatic peel 6–10 mm thick and dotted with oil glands, and pale, acid pulp in 8 to 10 segments. Klimek-Szczykutowicz and colleagues (Plants 2020) explain that the peel’s colored outer layer, the flavedo, holds the oil vesicles and carotenoid pigments. Major cultivars include Eureka and Lisbon, grown from the Mediterranean to California, Australia, and Argentina, and Femminello in Italy, which flowers and fruits through the year. Meyer lemon, which Morton calls a lemon × mandarin hybrid, and rough lemon (C. jambhiri) are lemon-like fruits rather than true lemons.

Each lemon product has its own chemistry. Lemon oil, Limonis aetheroleum in the European and US pharmacopoeias, is obtained by cold-pressing the fresh outer peel. Klimek-Szczykutowicz and colleagues report limonene at 69.9%, β-pinene 11.2%, γ-terpinene 8.21%, sabinene 3.9%, and myrcene 3.1%, with geranial (2.9%) and neral (1.5%), the two halves of citral, giving much of the lemony note. The oil also carries non-volatile furanocoumarins; one analysis detected 13, including bergapten, oxypeucedanin, and bergamottin. A 2013 Cosmetic Ingredient Review (CIR) summary lists oxypeucedanin at 0.005–0.073% and bergapten at 0.0001–0.0087% of lemon oil, far less bergapten than lime oil (0.17–0.33%). The juice is defined by citric acid: Penniston and colleagues (Journal of Endourology 2008) measured 1.44 g per fluid ounce in fresh lemon juice and 1.10 g in concentrate, against 0.03–0.22 g in ready-made lemonades and juice drinks. Morton’s tables give about 46 mg of vitamin C per 100 g of fresh juice and 129 mg in raw peel. The peel and juice contain flavanones such as hesperidin, naringin, and eriocitrin, which is more abundant in lemon than in other citrus fruits, plus diosmin and limonoids. Petitgrain oil, distilled from lemon leaves and twigs, is up to 50% citral (Morton).

The lemon reached the Mediterranean early and as a luxury. Langgut (HortScience 2017), reviewing ancient texts, art, and plant remains, found that citron was the first citrus to travel west and that the earliest lemon remains, from the Forum Romanum in Rome, date to the late first century BC or early first century AD; in antiquity both fruits were linked to elite gardens. Sour orange, lime, and pummelo arrived only in the 10th century AD, after the Islamic conquests, which implies that the lemon’s own hybrid origin lay farther east. Morton records that lemons were cultivated in Iraq and Egypt by 700 AD, reached Sicily before 1000, and were spread widely around the Mediterranean by Arabs between 1000 and 1150; they were prized for their medicinal virtues in the palace of the Sultan of Egypt and Syria in 1174–1193. Christopher Columbus carried lemon seeds to Hispaniola in 1493, lemons were grown in California by the 1750s and 1760s, and commercial groves in Florida and California began soon after 1870. In the 20th century, Guatemala and southern Mexico planted lemons mainly for their peel oil.

Lemon’s great medical story is scurvy. On 20 May 1747, aboard HMS Salisbury, the Scottish naval surgeon James Lind took 12 sailors with scurvy, kept them in the same quarters on the same diet, and gave pairs of them cider, elixir of vitriol (dilute sulfuric acid), vinegar, sea water, a medicinal paste, or two oranges and one lemon a day. The fruit ran out after six days, yet, as Lind wrote in his 1753 Treatise of the Scurvy, “the most sudden and visible good effects were perceived from the use of the oranges and lemons”: one sailor was fit for duty after six days and the other was appointed nurse to the rest (James Lind Library). Lind, who thought oranges preferable to lemons, never clearly recommended lemon juice to the Admiralty, and his boiled-down juice concentrate, or “rob,” was later shown to contain practically no vitamin C (Milne 2012). According to Tröhler, it was Gilbert Blane who in 1795 persuaded the Admiralty to issue lemon juice on a far more generous scale, after a fleet supplied with lemon juice preserved in alcohol reached Madras scurvy-free in 1793. Baron (Nutrition Reviews 2009) notes that when lime juice was substituted for lemon juice around 1860, scurvy returned, especially on polar expeditions.

Folk medicine used lemon widely. Klimek-Szczykutowicz and colleagues record traditional use of the juice for sore throats, fevers, rheumatism, high blood pressure, and chest pain, and of lemon oil taken on sugar for coughs in Romania. Morton notes that sweetened juice was given in Italy for gum and mouth inflammation and that lemon juice with honey, salt, or ginger was a common cold remedy, while warning that the habit of daily lemon juice in hot water as a laxative and cold preventive erodes tooth enamel. The peel has its own culinary tradition: limoncello, the Italian liqueur, is made by steeping lemon peel in alcohol, and the protected “Liquore di Limone della Costa d’Amalfi” must be made by cold maceration of peel from Amalfi Coast lemons, with at least 25% alcohol and 200–350 g of sugar per liter. Lemon’s modern health uses are more recent. Urologists were testing lemonade as a natural citrate source for kidney stones by the mid-1990s (Seltzer and colleagues 1996), and the National Center for Complementary and Integrative Health (NCCIH) now names lemon among the essential oils commonly used in aromatherapy.

How a lemon scent might ease nausea is not known. No specific receptor or pathway has been shown, and the effect, if real, may run through mood, attention, and expectation as much as pharmacology. Kiecolt-Glaser and colleagues (Psychoneuroendocrinology 2008) exposed 56 healthy adults to lemon oil, lavender oil, and water on separate visits, telling some what to expect and others nothing. Lemon reliably improved mood compared with water and lavender regardless of what people had been told, and norepinephrine stayed higher after a cold-water pain test, but lemon did not change cortisol, heart rate, blood pressure, skin barrier repair, or pain ratings. That pattern fits a pleasant, alerting scent rather than an anti-nausea drug. In the pregnancy trial, Yavari kia and colleagues noted that nausea fell in the placebo group too and that subjective outcomes are especially prone to placebo effects; they also observed that a scent pleasant to one person can be unpleasant to another, which matters for nausea, where smells are often triggers. A lemon scent is also hard to disguise, so participants in these trials may have guessed which group they were in.

For kidney stones the rationale is citrate. Citrate in urine binds calcium and slows the growth and clumping of calcium crystals, and the AUA’s 2026 guideline explains that fruits and vegetables raise urinary citrate because their organic acids, bound to potassium, magnesium, and calcium, are turned into bicarbonate in the liver, so the kidneys reabsorb less citrate. Lemon juice, however, delivers its citrate mostly as free citric acid, and the accompanying mineral seems to matter. In a controlled metabolic study, Odvina (Clinical Journal of the American Society of Nephrology 2006) gave 13 volunteers distilled water, orange juice, or lemonade with comparable citrate content; orange juice raised urinary pH and citrate, but lemonade did not. Koff and colleagues (Urology 2007) found in 21 stone formers that prescription potassium citrate, but not lemonade, significantly raised urinary citrate and pH. Lemonade’s other benefit is simply more fluid: in a review of 100 patients, Penniston and colleagues (Urology 2007) found that lemonade therapy raised urine volume by up to 763 ml a day.

Lemon oil’s chemistry explains both its use in Myrtol and its main hazard. Myrtol is a distillate of rectified eucalyptus, sweet orange, myrtle, and lemon oils in a 66:32:1:1 ratio, packed as 300 mg enteric-coated capsules (Seibel and colleagues, Planta Medica 2023). Paparoupa and Gillissen (Pharmacognosy Reviews 2016) name d-limonene, 1,8-cineole, and α-pinene as its main active markers and summarize studies showing mucus-thinning and airway-relaxing effects, but with lemon at 1% of the mix, its own contribution cannot be separated. The hazard comes from furanocoumarins (psoralens), which make skin react to ultraviolet light. In guinea pig tests summarized by the CIR, lemon oils at 50% and 100% strength were phototoxic under UVA light, the potency varied by region of origin, and oxypeucedanin and bergapten were identified as the responsible compounds. Lemon peel juice painted on rat skin caused a phototoxic reaction after as little as 2.5 minutes of sun, and sunscreen lessened but did not prevent it. Laboratory reports of antimicrobial, anti-inflammatory, and anticancer activity for lemon extracts (Klimek-Szczykutowicz) have not been tested in people.

Nausea and vomiting of pregnancy is lemon oil’s best-studied use. Yavari kia and colleagues (Iranian Red Crescent Medical Journal 2014) randomized 100 women at 6 to 16 weeks of pregnancy with mild to moderate nausea in Birjand, Iran, to lemon essential oil or a placebo, both given as drops on a cotton ball to sniff whenever they felt sick, alongside dietary advice. Over four days, scores on the Pregnancy-Unique Quantification of Emesis (PUQE-24) scale fell in both groups, but were significantly lower with lemon on the second and fourth days (p = 0.017 and 0.039), not on every day. The same research group (Safajou and colleagues 2020) tested a combined lemon and peppermint inhaler in 90 pregnant women and found lower scores than placebo from the second to the fourth day, though that design cannot show what lemon added. Rafiei and colleagues (Journal of Midwifery and Women’s Health 2026) found five studies of lemon aromatherapy in pregnancy; most reported less nausea and vomiting, but quality ranged from low to moderate, samples were small, and the authors called for better trials before any clinical recommendation.

After surgery and during cancer treatment, the trials are small. Rambod and colleagues (BMC Complementary Medicine and Therapies 2023) randomized 90 patients having surgery for leg fractures to lemon inhalation, repeated every two hours from the morning of surgery until 16 hours afterward, or a control group, and reported less pain, nausea, vomiting, and retching and less use of anti-sickness drugs. Sangi and colleagues (Iranian Journal of Pharmaceutical Research 2026) randomized 104 heart bypass patients to lemon scent or an odorless placebo, delivered before and for 72 hours after surgery, and reported lower pain and nausea scores and less delirium. Both were single-center trials in Iran. The 2018 Cochrane review by Hines and colleagues, covering 16 studies and 1,036 people, found that aromatherapy in general was no better than placebo for nausea severity after surgery, though people using it needed rescue anti-sickness medicine less often (risk ratio 0.60); both findings were low-quality evidence, and the abstract reports no separate result for lemon. In cancer care, a retrospective Austrian review of 66 palliative patients found adequate relief in 73% of 205 documented applications of lemon oil pads, without any comparison group (Kreye and colleagues 2022).

Kidney stone prevention is lemon juice’s main medical use. In 1996, Seltzer and colleagues (Journal of Urology) had 12 people with low urinary citrate (hypocitraturia) who could not take or tolerate prescription citrate drink 4 ounces of reconstituted lemon juice (5.9 g of citric acid) diluted to 2 liters of water through the day; after six days, urinary citrate rose from an average of 142 to 346 mg a day in 11 of them. Kang and colleagues (Journal of Urology 2007) reviewed 11 patients on lemonade for an average of 44 months; citrate rose by 383 mg a day and stone formation fell from 1.00 to 0.13 stones per patient per year, a difference that was not statistically significant. Aras and colleagues (Urological Research 2008) gave 30 hypocitraturic patients about 85 ml of fresh lemon juice a day, potassium citrate, or dietary advice for three months; urinary citrate rose about 2.5-fold, 3.5-fold, and 0.8-fold, respectively. Not every study agreed: in Koff’s 21-person crossover trial, lemonade did not significantly raise citrate, and a 2016 meta-analysis by Pachaly and colleagues concluded that larger trials are needed to show whether such dietary measures prevent stones.

The one randomized trial with stone recurrence as its outcome was disappointing. Ruggenenti and colleagues (EClinicalMedicine 2022) randomized 203 adults with recurrent calcium oxalate stones in Bergamo, Italy, all on a standard diet, to 60 ml of fresh lemon juice twice daily or no supplement. Over two years, stones recurred in 21 of 100 people on lemon juice and 32 of 103 controls, a hazard ratio of 0.62 that was not statistically significant (p = 0.089). Only 48% were still taking the juice at two years; in an exploratory analysis of the first year, recurrence was 10 versus 22 (hazard ratio 0.43), but urinary citrate and pH never differed between groups, and 84% of participants had normal citrate to begin with. The AUA’s 2026 guideline asks stone formers to drink enough, preferably water, to pass at least 2.5 liters of urine a day, and for calcium stone formers with low citrate it recommends a diet rich in fruits and vegetables, as expert opinion, without singling out lemon. Its 2014 guideline notes that randomized trials support prescription potassium citrate for these patients.

Myrtol is the combination product in which lemon oil appears. Gillissen and colleagues (Drug Research 2013) randomized 413 adults with acute bronchitis to Myrtol 300 mg four times daily or placebo for up to two weeks; after about a week, coughing fits had fallen by 62.1% with Myrtol and 49.8% with placebo. Pfaar and colleagues (Laryngoscope 2023) randomized 463 people with acute viral rhinosinusitis to one capsule four times daily or placebo; symptom scores improved significantly from day 4, symptoms resolved about three days sooner, and both treatments were well tolerated. These results apply to the finished product, in which lemon oil is 1 part in 100, and say nothing about lemon oil on its own; eucalyptus and sweet orange oils make up 98% of the blend. Beyond these uses, the lemon’s antimicrobial, anti-inflammatory, and anticancer properties reported in laboratory studies remain untested in people, and NCCIH reports that in one controlled study, smelling lemon lifted mood but did not change stress markers or pain.

Inhaled lemon oil has no standard dose; the trials used simple, short sniffs. In the pregnancy trial, women put two drops of the study solution on a cotton ball, held it about 3 cm from the nose, breathed in deeply three times when they felt nauseated, and repeated once after five minutes if needed. The lemon and peppermint trial used three drops on a cotton ball at the same distance. The surgical trials repeated inhalation every two hours, and the palliative care unit placed lemon oil on cotton pads. Use the oil on a tissue, cotton ball, or personal inhaler rather than on the skin, stop if the smell makes nausea worse, and remember that a room diffuser exposes everyone nearby, including children. A bottle of lemon essential oil sold for aromatherapy is not labeled or dosed for swallowing, so keep it out of food and drinks. Myrtol contains rectified (redistilled) lemon oil inside an enteric-coated capsule, a very different product from an aromatherapy bottle.

Lemon juice for kidney stones has been studied in a few set amounts. Seltzer’s lemonade was 4 ounces (about 120 ml) of reconstituted lemon juice mixed into 2 liters of water and sipped through the day. The Italian recurrence trial used 60 ml of freshly squeezed juice twice daily, and Aras and colleagues about 85 ml of fresh juice a day, calculated to supply about 60 mEq of citrate. Penniston’s measurements matter when shopping: fresh lemon juice and bottled concentrate supply roughly 1.1 to 1.4 g of citric acid per fluid ounce, while ready-to-drink lemonades and juice drinks supplied only 0.03 to 0.22 g, so a glass of commercial lemonade is not the same as lemonade therapy, and sweetened versions add sugar. Because the evidence is limited and most of it comes from people with low urinary citrate, anyone who has had a stone is best advised to have the 24-hour urine testing the AUA recommends for people at higher risk and to agree on a plan with their urologist or dietitian rather than relying on lemon water alone.

Myrtol is sold in Europe and elsewhere as GeloMyrtol forte, a 300 mg enteric-coated soft capsule; the bronchitis trial used one capsule four times daily for up to two weeks. Zhao and colleagues (Patient Preference and Adherence 2016) noted that the prescribing information calls for an empty stomach and found that taking a capsule after a meal more than doubled absorption of its marker compound in healthy volunteers, so the two ways of taking it are not interchangeable; follow the label. Lemon in food and drink needs no special guidance, and the FDA’s GRAS list covers lemon and lemon peel oils as flavorings. Peel used for zest, candied peel, or limoncello comes into contact with the oil glands, so wash fruit well and keep zesting hands out of strong sun until washed. Keep all essential oils tightly closed and stored out of children’s sight and reach, apart from medicines, and never swallow aromatherapy oil or add it to drinking water.