Citric acid plays a central role in how your body produces energy, and it also affects your teeth, kidneys, skin, and mineral absorption depending on how you encounter it. You consume it every time you eat citrus fruit, drink a soda, or take a gummy vitamin. Fresh lemon juice contains about 48 grams per liter, lime juice about 46 grams per liter, and orange juice around 9 to 17 grams per liter depending on the source. Here’s what it actually does once it enters your body.
It Fuels Your Cells’ Energy Production
Citric acid is the starting molecule of the citric acid cycle, sometimes called the Krebs cycle, which is the process your cells use to convert food into usable energy. This cycle runs inside the mitochondria of nearly every cell in your body and represents the final stage of breaking down carbohydrates, fats, and proteins for fuel.
The cycle works in eight steps. First, a molecule called acetyl-CoA (derived from the food you eat) combines with another molecule to form citrate, the ionized form of citric acid. From there, the citrate is progressively broken down through a series of chemical reactions that release carbon dioxide and, more importantly, generate the reduced coenzymes your cells need to power the electron transport chain. That chain is where the vast majority of your body’s ATP, its primary energy currency, is actually produced. Without citric acid initiating this cycle, your cells would have no efficient way to extract energy from food.
The citric acid you eat in a lemon doesn’t directly slot into this cycle in any meaningful way. Your body synthesizes its own citrate internally. But the cycle itself is named after this compound because citrate is its essential first product.
It Helps Prevent Kidney Stones
Citric acid is one of the most effective natural compounds for reducing kidney stone risk. Once absorbed, it increases citrate levels in your urine, which prevents stones through two distinct mechanisms. First, citrate binds to calcium in the urine, lowering the concentration of free calcium available to crystallize. Second, it attaches directly to calcium oxalate crystals that have already started forming and blocks them from growing larger.
This is why doctors often recommend lemon juice or citrate supplements for people prone to calcium oxalate stones, the most common type. The high citric acid content in lemon and lime juice (48 and 46 grams per liter, respectively) makes them particularly useful. Even commercially available lemon juice concentrates contain 34 to 39 grams per liter. Drinking diluted lemon water regularly is a simple, low-cost strategy to raise urinary citrate.
It Improves Mineral Absorption
Citric acid enhances your body’s ability to absorb certain minerals, particularly non-heme iron, the type found in plant foods like spinach, beans, and fortified cereals. In one study on an oat-based beverage, adding citric acid improved iron absorption by 54%. This happens because citric acid binds to iron in the digestive tract and keeps it in a soluble form that your intestinal lining can take up more easily.
This is practically useful if you eat a plant-heavy diet. Squeezing lemon over iron-rich foods or pairing them with citrus isn’t just a flavor choice; it has a measurable effect on how much iron your body retains.
It Erodes Tooth Enamel
Citric acid is one of the most aggressive dietary acids when it comes to dental erosion. Tooth enamel begins to dissolve below a critical pH threshold, and citric acid solutions sit well below that line. A 6% citric acid solution has a pH of about 1.88, and even a 1% solution comes in at 2.55. Research using flow cells that simulate drinking found that enamel erosion begins within 30 to 90 seconds of exposure.
Even when citric acid is buffered to a commercially relevant pH of 3.8 (closer to what you’d find in a soft drink or sports drink), it still dissolves enamel surfaces. This means sipping on citrus juices, lemonade, or sour candies throughout the day gives the acid repeated contact with your teeth, compounding the damage over time. Drinking through a straw, rinsing with water afterward, and avoiding brushing immediately after acidic exposure (which can spread softened enamel) all reduce the risk.
It Can Worsen Acid Reflux
If you have gastroesophageal reflux, citric acid is likely making it worse. The high acidity of citrus fruits and juices relaxes the esophageal sphincter, the muscular valve between your esophagus and stomach that normally keeps acid from traveling upward. When that sphincter loosens, stomach acid rises into the esophagus and causes the burning sensation associated with reflux. Grapefruit and orange juice are common triggers, but any concentrated source of citric acid can have this effect.
What It Does for Your Skin
Citric acid is an alpha hydroxy acid (AHA), and in topical skincare products it acts as a chemical exfoliant. At low concentrations of 5 to 10%, the range found in most daily skincare products, it promotes mild exfoliation and helps maintain skin texture and brightness. At higher concentrations of 20 to 30%, it’s used in professional chemical peels for more significant resurfacing.
Beyond exfoliation, citric acid has been shown to increase collagen synthesis, improve the quality of elastic fibers, and boost the density of water-binding molecules in the skin that help it stay hydrated and firm. It also lightens post-inflammatory hyperpigmentation (the dark spots left behind after acne or injury) by regulating the enzyme responsible for melanin production. Formulations range from 2% to 70% across cleansers, lotions, creams, and gels.
Natural vs. Manufactured Citric Acid
Nearly all citric acid added to packaged foods and beverages is manufactured through fermentation using a mold called Aspergillus niger, not extracted from citrus fruit. The molecular formula is identical: C₆H₈O₇. However, the manufacturing process may leave behind trace proteins or byproducts from the mold, and a small number of people appear to react to these contaminants.
A case report published in Toxicology Reports documented four patients who experienced significant inflammatory reactions, including respiratory symptoms, joint pain, irritable bowel symptoms, and muscle pain, after consuming foods and beverages containing manufactured citric acid. None of them developed symptoms when consuming natural citric acid from lemons and limes. The researchers hypothesized that residual proteins or byproducts from A. niger in the manufactured product triggered elevated inflammatory markers or an immune response with repeated exposure over time.
This is still a small body of evidence, and most people consume manufactured citric acid daily without noticeable problems. The Joint FAO/WHO Expert Committee on Food Additives assigned citric acid and its salts an acceptable daily intake of “not limited” in 1973, meaning they found no evidence of harm at typical dietary levels. But if you notice unexplained inflammatory symptoms that seem tied to processed foods, manufactured citric acid is worth investigating as a possible contributor.
Effect on Blood Chemistry
Citric acid is sometimes described as “alkalizing” in wellness circles, but the reality is more straightforward. In laboratory studies where citric acid was added directly to blood samples at increasing concentrations, it progressively lowered blood pH (making it more acidic), reduced bicarbonate levels, and increased carbon dioxide. This is why citric acid is used medically as a regional anticoagulant in certain blood-processing procedures: it binds ionized calcium, which is essential for clotting.
In normal dietary amounts, though, your body’s buffering systems neutralize ingested citric acid efficiently. Your kidneys and lungs maintain blood pH within a tight range of 7.35 to 7.45 regardless of what you eat. Drinking lemon water will not meaningfully change your blood pH.