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Lactic acid

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Lactic acid
Lactic-acid-skeletal.pngLactic-acid-ball and stick.png
Systematic name 2-hydroxypropanoic acid
Other names Milk acid
Molecular formula C3H6O3
Molar mass Molar mass::90.08 g/mol
Appearance colorless
CAS number

CAS number::50-21-5
L: CAS number::79-33-4
D: CAS number::10326-41-7
D/L: CAS number::598-82-3

Density and phase Density::1.1478 g/ml, liquid
Solubility in water fully miscible
Melting point [[Melting point::L: 53°C
D: 53°C
D/L: 16.8°C]]
Boiling point Boiling point::122°C
Acidity (pKa) 3.86
Viscosity 2.40 cP at 100°C
MSDS Material safety data sheet
Main hazards irritant, corrosive
NFPA 704

NFPA 704 svg.png

Related compounds
Other anions lactate
Related carboxylic acids acetic acid
glycolic acid
propionic acid
3-hydroxypropanoic acid
malonic acid
butyric acid
hydroxybutyric acid
Related compounds 1-propanol
sodium lactate
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Disclaimer and references

Lactic acid is an organic chemical compound found naturally in the bodies of humans and animals. Although lactic acid occurs within the body, it was first discovered as a byproduct of spoiled milk in 1780 by Carl Wilhelm Scheele, a chemist from Sweden. [1]. For this reason, lactic acid is occasionally called milk acid. The main biological purpose of lactic acid is to aid in energy production in the muscles of humans and animals. Fermentation techniques are able to isolate lactic acid for use in a wide range of commercial and pharmaceutical products. Like most acids, lactic acid can be dangerous if it comes into contact with the eye.


Lactic acid is a relatively weak acid that exists in the liquid phase as one of the smallest molecules with a carbon located asymmetrically in its elemental composition [2]. Lactic acid also serves as an effective regulator of pH levels [3]. The acid can form solid white crystals [2]. It fully dissolves when placed into water that has been heated to 25ºC [4]. When submerged in water, lactic acid dissolves completely. It is a relatively safe acid, but can irritate the eyes and skin if exposed and causes heavy irritation if breathed in or ingested [5]. Lactic acid has no scent or color.­ Lactic acid has two main forms, D(-) and L(+). The L(+) form is the most active form found in most organic creatures, such as animals and humans, while the D(-) form can also be traced in organic creatures [2].

Production in Living Things (Metabolism)

Main Article: Lactic acid metabolism
A small sample of lactic acid

Lactic acid is classified as an organic acid, meaning it is produced within a living organism as a means of maintaining health. Lactic acid occurs naturally within the bodies of several creatures, including humans. Primarily lactic acid is found in the muscles of an organism, but in some creatures such as humans, lactic acid can also be found in the liver for metabolic purposes, and in the urine. Many microorganisms produce lactic acid as well, the most common of which being different species of fungi and bacteria. Several species of these microorganisms can be manipulated in laboratories to produce lactic acid for commercial purposes. For example, microorganisms such as R. arrhizus directly transform starch into pure lactic acid via enzyme conversion. Another common method of manufacturing lactic acid by taking advantage of microorganisms remains fermentation through yeast. While these methods remain the most efficient ways of biotechnologically producing lactic acid in a laboratory setting, the process still varies in its reliability and efficiency [6].


Lactic acid occurs naturally as a result of fermentation. The acid was first discovered in spoiled milk, but ferments in many other foods as well. Bacteria and fungi are responsible for fermenting the lactic acid which provides a tangy sourness to foods such as sauerkraut and kimchi. Lactic acid fermentation also aids in the formation of dairy products such as yogurt. There are several benefits to adding lactic acid to a food by fermentation. Food stays safe and lasts a longer amount of time, increases the nutrient amount of the food, and helps to prevent disease [7]. Lactic acid also is added to processed meats and salads for these same purposes, but also aid in developing flavor and pathogen regulation. As an electrolyte, lactic acid is commonly added to health supplements to restore the natural elements a body needs [6]. Lactic acid also is typically used as an additive in hand sanitizers due to its antimicrobial capabilities [3]. The textile industry utilizes lactic acid as a agent that allows fabrics to absorb dyes [8]. The cosmetic industry also takes advantage of lactic acid. Lactic acid is used widely in several types of skin moisturizers and hydration creams. The property of lactic acid to inhibit the creation of tyrosinase in the skin coupled with the fact that lactic acid does not readily irritate the skin helps to achieve this effect [6] [3].

In human and most animal bodies, lactic acid is used as a means of removing excess hydrogen ions in muscles. Lactic acid removes these ions in order to balance pH levels as well. This topic is described in greater detail later.

Muscle Activity

intense physical activity spurs the production of lactic acid

Lactic acid is generated by cells when an organism undergoes intense physical exercise. In order to supply necessary energy, the body burns carbohydrates to make Adenosine Triphosphate (or ATP). Energy is then provided to the muscles when ATP is broken down. Although oxygen is usually supplied to cell in order to make ATP, at times oxygen can not be sent to specific areas soon enough. [9]. Later on, the liver converts the lactic acid back into glucose, which can then be used to make ATP when sufficient oxygen is present.[10]. The accumulation of lactic acid in the muscles increases the acidity of the muscles cells. This higher acidity causes fatigue, which can persist in the muscles for several hours after the completion of exercise [11].


Brief description on lactic acid buildup in muscles.


  1. .History of Lactic Acid. lactic-acid.Unkown Author. Web. Accessed 17 March 2013.
  2. 2.0 2.1 2.2 .History of Lactic Acid. Lactic.Unknown Author. Web. Accessed 27 February 2013.
  3. 3.0 3.1 3.2 .APPLICATIONS OF LACTIC ACID & SALTS. tripod. Unknown Author. Web. Accessed 17 March 2013.
  4. . Lactic acid. Environmental Protection Agency.Unknown Author. Web. Accessed 27 February 2013.
  5. .Lactic acid. Sciencelab.Unknown Author. Web. Accessed 27 February 2013.
  6. 6.0 6.1 6.2 .Wee, Young-Jung; Kim, Jin-Nam; Ryu, Hwa-Won.Biotechnological Production of Lactic Acid and Its Recent Applications. ftb. Web. Finalized 12 March 2006.
  7. Lactic acid fermentation. Tempeh.Unknown Author. Web. Accessed 27 February 2013.
  8. .Gotlib, Louis.Lactic Acid - Uses Of Lactic Acid. jrank. Web. Accessed 17 March 2013.
  9. .Roth, Stephen.Why does lactic acid build up in muscles? And why does it cause soreness?. scientific American.Web. Accessed 17 March 2013.
  10. .Mackenzie, Brian. Lactic Acid. Brianmac. Web. Last Modified 18 October 2012.
  11. .Quinn, Elizabeth. Lactic acid does more than cause fatigue. About. Web. Updated November 21, 2003.