Citric Acid

Overview

Citric acid is a naturally occurring weak organic acid found predominantly in citrus fruits such as lemons, limes, oranges, and grapefruits. Chemically, it is a colorless crystalline compound with the formula C₆H₈O₇. It plays a crucial role in biochemistry as an intermediate in the citric acid cycle (Krebs cycle), which is essential for energy production in aerobic organisms. Industrially, citric acid is mass-produced—over two million tons annually—and widely used as a flavoring agent, acidifier, preservative, and chelating agent in food, pharmaceutical, and cosmetic industries. Historically, it has been valued for its sour taste and preservative properties in food and beverages, as well as for its antioxidant and anticoagulant functions in medicine.¹²

Forms and Variations

Citric acid is commonly available in several forms including anhydrous powder, monohydrate crystals, and liquid solutions. In supplements and industrial applications, it is often found as pure citric acid or as salts known as citrates (e.g., trisodium citrate). Citrates are used for their buffering and chelating properties. In cosmetics and personal care, citric acid is formulated as an alpha hydroxy acid (AHA) for exfoliation and pH adjustment. The choice of form depends on the intended use: powders and crystals are preferred for food and pharmaceutical manufacturing, while liquid forms are common in cleaning products and cosmetics. Citrates are favored in medical and nutritional supplements for their bioavailability and buffering capacity.²⁴

Dosage and Administration

Citric acid is generally recognized as safe (GRAS) when used in food and cosmetic products at typical concentrations. There is no established dietary requirement since it is not a vitamin or mineral. In food, it is used at concentrations up to 5-6% to impart sourness and preserve freshness. In supplements, citrate salts are dosed according to the mineral content they provide (e.g., calcium citrate). For cosmetic use, concentrations of citric acid typically range from 1% to 10% depending on the product type, with higher concentrations used in chemical peels under professional supervision. It is best administered dissolved in water or incorporated into formulations where it can adjust pH or act as a chelating agent.¹⁴

Scientific Research and Mechanism of Action

Citric acid functions primarily as a weak acid that partially dissociates in aqueous solutions, contributing to acidity and sour taste. Its chelating ability allows it to bind metal ions such as calcium, which is exploited in food preservation and anticoagulation by preventing blood clotting. In biochemistry, citric acid is a key intermediate in the citric acid cycle, facilitating cellular energy production by oxidizing carbohydrates, fats, and proteins. Research highlights its antioxidant properties, which help stabilize active ingredients in pharmaceuticals and protect skin cells from free radical damage in cosmetics. As an alpha hydroxy acid, citric acid promotes exfoliation by loosening dead skin cells, improving skin texture and tone. Current studies continue to explore its roles in enhancing product stability, skin health, and potential therapeutic applications.¹²⁴

Benefits and Potential Uses

Citric acid offers multiple benefits across various fields. In food, it acts as a natural preservative, flavor enhancer, and pH adjuster, extending shelf life and improving taste. In pharmaceuticals, it stabilizes active ingredients and serves as an anticoagulant by chelating calcium in blood. In cosmetics, it functions as an exfoliant and antioxidant, promoting skin renewal, reducing pigmentation, and protecting against oxidative damage. It also improves hair manageability by adjusting pH in shampoos and rinses. Additionally, citric acid is widely used in household cleaning products to remove hard water deposits and soap scum due to its chelating and acidic properties. Its effervescent reaction with baking soda is popular in bath bombs, creating a fizzing effect for spa-like experiences.¹⁴

Side Effects and Risks

Citric acid is generally safe when used appropriately; however, excessive exposure may cause mild irritation to the skin, eyes, or mucous membranes due to its acidic nature. Ingesting large amounts can lead to gastrointestinal discomfort such as stomach pain or diarrhea. People with sensitive skin or allergies should exercise caution when using cosmetic products containing citric acid, as it may cause redness or irritation. Those with kidney disorders should consult healthcare providers before using citrate supplements, as altered mineral balance may affect kidney function.⁴

Interactions and Precautions

Citric acid can interact with certain medications by altering absorption or chelating metal ions, potentially affecting drug efficacy. For example, it may influence the absorption of calcium or magnesium supplements. Individuals with kidney disease or metabolic disorders should use citrate-containing supplements under medical supervision. In medical procedures, citric acid is used as an anticoagulant in blood collection tubes by chelating calcium, which prevents clotting. Care should be taken to avoid excessive intake or exposure in these contexts.¹

Impact on Biomarkers

Supplementation with citrate salts can influence blood and urine biomarkers by altering mineral levels, particularly calcium and citrate concentrations. Citrate acts as a natural inhibitor of kidney stone formation by binding calcium, thus increasing urinary citrate levels, which is beneficial in preventing calcium oxalate stones. Blood calcium levels may be affected transiently with high citrate intake. Monitoring is advised in clinical settings when citrate supplements are used.²

Overdose and Toxicity

Overconsumption of citric acid or citrate salts is uncommon but can lead to symptoms such as stomach upset, acid reflux, or metabolic alkalosis in extreme cases. Toxicity is rare due to its weak acidity and rapid metabolism. The safe upper limit has not been firmly established but typical dietary and supplemental use is considered safe. Excessive intake should be avoided to prevent gastrointestinal irritation or electrolyte imbalances.¹

Disclaimer

The information provided in this document is for educational purposes only and does not constitute medical advice. It is essential to consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.