Health Effects of Benzoic Acid, Sodium Benzoate, and Benzene
Benzoic Acid and Benzoates
Benzoic acid and benzoates are common additives to food, drinks, and other products. They are useful chemicals in manufactured products because they kill or inhibit both bacteria and fungi and can act as preservatives. In general, the chemicals are considered to be safe when they're used in small quantities. There are some situations in which they may be harmful, however.
Benzoic acid was first obtained from the resin of trees belonging to the Styrax genus. The fragrant resin smells like vanilla and is sometimes known as gum benzoin. Today benzoic acid is often made in the laboratory from other chemicals instead of being extracted from gum benzoin.
Benzoates are derived from benzoic acid and are more commonly used as food preservatives than the acid. Some people develop allergy-like symptoms when they are exposed to sodium benzoate. When the chemical reacts with vitamin C (ascorbic acid) in drinks under certain conditions, benzene may be produced. Benzene is a carcinogen. A carcinogen is a substance that is capable of causing cancer.
Difference Between Benzoic Acid and Sodium Benzoate
Pure benzoic acid is a white to colourless solid which consists of crystalline needles or scales. It's a member of the carboxylic acid family and has the molecular formula C6H5COOH. Benzoic acid is only slightly soluble in water. Sodium benzoate is structurally related to benzoic acid and has the formula C6H5COONa. It exists as a granular powder and is more soluble in water than the acid.
Sodium benzoate is more commonly used as a food preservative than benzoic acid due to its greater solubility in water. Benzoic acid is a more effective germ killer, however. The benzoate form of the chemical is converted into the acid form in our stomach and absorbed into the body through the lining of the small intestine.
Benzoic acid can be changed into sodium benzoate, and vice versa. If the environment is suitably acidic, benzoic acid predominates. If the environment is not sufficiently acidic and sodium ions are present—as they often are—sodium benzoate predominates.
Benzoic Acid in Food and Other Products
Benzoic acid is found in many plants. Significant amounts have been found in some fruits—especially berries—as well as in yogurt, certain spices, and honey. Artificial benzoic acid is added to food and to products such as toothpastes, shampoos, cosmetics, and medicines in order to prevent microbial growth.
Benzoic acid is most effective as a food preservative in acidic food. It seems to harm microbes by preventing them from fermenting glucose, but it may have other effects on the microbes as well.
Gum Benzoin and Tincture of Benzoin
Gum benzoin is also known as benzoin resin, gum benjamin, and kemenyan. It's rich in natural benzoic acid and smells pleasant. Two types are available commercially—Siam benzoin and Sumatra benzoin. Siam benzoin is used mainly in the perfume industry while Sumatra benzoin is used in natural health care.
Siam benzoin is produced by wounding the bark of a tree called Styrax tonkinensis, which is found in Vietnam, Cambodia, Laos, and Thailand. Sumatra benzoin is obtained from the bark of Styrax benzoin, which is native to Sumatra. The injury to the bark of either tree causes a yellow liquid to be released. The liquid hardens into a sticky yellow or red-brown solid.
Tincture of Benzoin
Tincture of benzoin is made by dissolving gum benzoin in alcohol. Compound Benzoin Tincture, Compound Tincture of Benzoin, and Friar's Balsam are three different names that refer to the same product. This product contains gum benzoin and alcohol as well as storax, Tolu balsam, and aloe. Storax is a resin exuded by a type of sweetgum tree and balsam is another plant resin.
Uses of Compound Benzoin Tincture
Compound Benzoin Tincture (CBT) is a sticky liquid that is applied to skin to improve the adhesion of medical tape and bandages. It's sometimes applied to skin areas that are subject to high friction because it's thought to reduce the chance of blister or ulcer formation.
Some people inhale steam from hot water containing CBT to relieve the congestion of a cold. Care is needed when using this product because it can act as a respiratory irritant as well as a skin and gastrointestinal irritant.
Potential Dangers of Benzoic Acid
Like most chemicals that have toxic properties, the effects of benzoic acid depend on its concentration. At the low concentrations found in plants and foods, the chemical isn't dangerous for most people. Once it's eaten or produced, benzoic acid is absorbed through the lining of the digestive tract and eventually converted into hippuric acid, which is excreted in the urine.
According to the Material Safety Data Sheet (MSDS) that is created for chemicals, benzoic acid can irritate the eyes, skin, lungs, and digestive tract. Most people aren't exposed to high enough concentrations to experience this irritation, but people who work with the pure chemical or with concentrated mixtures need to be careful. Benzoic acid can enter the body through the skin as well as the digestive and respiratory tracts.
Potential Dangers of Sodium Benzoate
There are several ways in which sodium benzoate can be harmful to people. For example, it can cause pseudoallergy symptoms in sensitive people. A pseudoallergy resembles an allergy in its presentation, but unlike a true allergy it doesn't involve an immune response.
A skin rash, itching, a runny nose, and congested airways are possible symptoms of a sodium benzoate pseudoallergy. If a person is asthmatic or has a tendency to develop hives, these problems may become worse after exposure to the chemical. It's thought that a negative response to sodium benzoate is rare in people who don't already have a true allergy. The chemical may play a role in increasing hyperactivity in children, however, although this is unproven.
When sodium benzoate reacts with ascorbic acid (vitamin C) in the presence of heat, light, and metallic ions, benzene forms. This reaction may happen in soft drinks that contain the chemicals. This is worrying, since benzene is a carcinogen. In the United States, the FDA (Food and Drug Administration) is aware of the problem. Between 2005 and 2007 the FDA discovered that some soft drinks contained benzene above the allowable level. Since this discovery, many manufacturers have reformulated their products to reduce the amount of benzene.
Benzene Properties and Uses
We are exposed to benzene from a variety of sources, including gasoline at gas stations, car exhausts, emissions from industries that burn coal or oil, emissions from other industrial processes, and cigarette smoke. It's important to avoid adding to the benzene load whenever we can to prevent reaching a critical level that harms our bodies.
Benzene Structure and Potential Dangers
Benzene has many important uses. Before its dangers were understood it was even used as a reactant in school chemistry experiments. Now it's generally used with caution and only by chemists who know how to handle it.
Benzene was discovered by Michael Faraday in 1825. It contains only carbon and hydrogen atoms and is therefore classified as a hydrocarbon. The benzene molecule is a six sided ring, as shown in the diagram above. The single lines represent single bonds holding atoms together and the double lines represent double bonds. Although benzene is often represented by this diagram, chemists have discovered that the bonding between the atoms is not as simple and clearcut as shown in the illustration.
Benzene exposure may produce acute (immediate) effects if a person is exposed to a large amount of the chemical. These effects include a headache, dizziness, vomiting, muscle tremors, a rapid or irregular heartbeat, drowsiness, and loss of consciousness. Exposure to a very high concentration of benzene can be deadly.
Exposure to benzene over a longer period of time can affect the bone marrow, decreasing its production of red blood cells and causing anemia. It can also weaken the immune system. In addition, long term exposure to benzene increases the risk of leukemia.
Simplfied Benzoic Acid Structure
Although the benzene molecule is dangerous, slightly altered forms of the molecule form part of many larger and generally harmless molecules, including aspirin. Benzoic acid and the various types of benzoates contain the benzene ring but have different atoms attached to one place on the ring. The change in structure removes the toxicity of benzene.
Safety of Benzoic Acid, Sodium Benzoate, and Benzene
Most people don't need to worry about benzoic acid and benzoates in food, drinks, and other sources, since the chemicals are usually present in small amounts. In addition, most people aren't exposed to high levels of benzene.
Some people do need to be concerned about benzoic acid and sodium benzoate, however, and should reduce their exposure to both substances. It's also advisable for everyone to avoid exposure to benzene as much as possible. We should all be aware of the potential dangers of these three structurally related chemicals.
References and Further Reading
© 2012 Linda Crampton