Chemical Burns

Updated: Dec 15, 2017
  • Author: Robert D Cox, MD, PhD; Chief Editor: Joe Alcock, MD, MS  more...
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Overview

Background

Chemical burns can be caused by acids or bases that come into contact with tissue. Acids are defined as proton donors (H+), and bases are defined as proton acceptors (OH-). Bases also are known as alkalis. Both acids and bases can be defined as caustics, which cause significant tissue damage on contact. The strength of an acid is defined by how easily it gives up the proton; the strength of a base is determined by how avidly it binds the proton. The strength of acids and bases is defined by using the pH scale, which ranges from 1-14 and is logarithmic. A strong acid has a pH of 1, and a strong base has a pH of 14. A pH of 7 is neutral.

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Pathophysiology

Most acids produce a coagulation necrosis by denaturing proteins, forming a coagulum (eg, eschar) that limits the penetration of the acid. Bases typically produce a more severe injury known as liquefaction necrosis. This involves denaturing of proteins as well as saponification of fats, which does not limit tissue penetration. Hydrofluoric acid is somewhat different from other acids in that it produces a liquefaction necrosis.

The severity of the burn is related to a number of factors, including the pH of the agent, the concentration of the agent, the length of the contact time, the volume of the offending agent, and the physical form of the agent. The ingestion of solid pellets of alkaline substances results in prolonged contact time in the stomach, thus, more severe burns. In addition, concentrated forms of some acids and bases generate significant heat when diluted or neutralized, resulting in thermal and caustic injury.

The long-term effect of caustic dermal burns is scarring, and, depending on the site of the burn, scarring can be significant. Ocular burns can result in opacification of the cornea and complete loss of vision. Esophageal and gastric burns can result in stricture formation. An oral burn is shown in the images below.

Caustic oral burns. Caustic oral burns.
Caustic burns of tongue. Caustic burns of tongue.
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Etiology

A large number of industrial and commercial products contain potentially toxic concentrations of acids, bases, or other chemicals that can cause burns. [1, 2] Some of the more common products are listed as follows:

Acids

Sulfuric acid is commonly used in toilet bowl cleaners, drain cleaners, metal cleaners, automobile battery fluid, munitions, and fertilizer manufacturing. Concentrations range from 8% acid to almost pure acid. The concentrated acid is very viscous and more dense than water. It also generates significant heat when diluted. These attributes make sulfuric acid an effective drain cleaner. Concentrated sulfuric acid is hygroscopic. Thus, it produces dermal injuries by dehydration, thermal injury, and chemical injury.

Nitric acid is commonly used in engraving, metal refining, electroplating, and fertilizer manufacturing.

Hydrofluoric acid is commonly used in rust removers, tire cleaners, tile cleaners, glass etching, dental work, tanning, semiconductors, refrigerant and fertilizer manufacturing, and petroleum refining. This is a weak acid, and, in dilute form, it will not cause immediate burning or pain on contact.

Hydrochloric acid is commonly used in toilet bowl cleaners, metal cleaners, soldering fluxes, dye manufacturing, metal refining, plumbing applications, swimming pool cleaners, and laboratory chemicals. Concentrations range from 5-44%. Hydrochloric acid is also known as muriatic acid.

Phosphoric acid is commonly used in metal cleaners, rustproofing, disinfectants, detergents, and fertilizer manufacturing.

Acetic acid is commonly used in printing, dyes, rayon and hat manufacturing, disinfectants and hair wave neutralizers. Vinegar is dilute acetic acid.

Formic acid is commonly used in airplane glue, tanning, and cellulose manufacturing.

Chloroacetic acids

Monochloroacetic acid is used in the production of carboxymethylcellulose, phenoxyacetates, pigments, and some drugs. It has significant systemic toxicity because it enters and blocks the tricarboxylic acid cycle, inhibiting cellular respiration. It is highly corrosive.

Dichloroacetic acid is used in manufacturing chemicals. It is a weaker acid than trichloroacetic acid, and it does not inhibit cellular respiration.

Trichloroacetic acid is used in laboratories and in chemical manufacturing. It is highly corrosive and "fixes" tissues it contacts. It does not inhibit cellular respiration.

Phenol and cresols

Phenol, also known as carbolic acid, is a weak organic acid used in the manufacture of resins, plastics, pharmaceuticals, and disinfectants.

Cresols are dihydroxybenzenes that are used as wood preservatives, degreasing agents, and chemical intermediates. These substances are very irritating to the skin and can be absorbed through the skin to produce systemic toxicity.

Bases

Sodium hydroxide and potassium hydroxide are used in drain cleaners, oven cleaners, Clinitest tablets, and denture cleaners. They are extremely corrosive. Clinitest tablets contain 45-50% sodium hydroxide (NaOH) or potassium hydroxide (KOH). Solid or concentrated NaOH or KOH is more dense than water and generates significant heat when diluted. Both the heat generated and the alkalinity contribute to burns.

Calcium hydroxide also is known as slaked lime. It is used in mortar, plaster, and cement. It is not as caustic as NaOH, KOH, or calcium oxide.

Calcium oxide, also known as quicklime, is the caustic ingredient in cement. It generates heat when diluted with water and can produce a thermal or caustic burn.

Sodium and calcium hypochlorite are common ingredients in household bleach and pool chlorinating solution. Pool chlorinators also contain NaOH and have a pH around 13.5, making them very caustic. Household bleach has a pH around 11 and is much less corrosive.

Ammonia is used in cleaners and detergents, as a fertilizer, and as an industrial cleaner and sterilizing agent. The dilute form is not highly corrosive. Gaseous anhydrous ammonia is used in a number of industrial applications, particularly in fertilizer manufacturing. It is very hygroscopic (has a high affinity for water). It produces injury by desiccation and heat of dilution, in addition to causing a chemical burn. It can cause severe skin burns as well as pulmonary injury if inhaled.

Phosphates commonly are used in many types of household detergents and cleaners. Substances include tribasic potassium phosphate, trisodium phosphate, and sodium tripolyphosphates.

Silicates include sodium silicate and sodium metasilicate. They are used to replace phosphates in detergents. Dishwashing detergents are alkaline, primarily to builders such as silicates and carbonates. They are moderately corrosive.

Sodium carbonate is used in detergents. It is moderately alkaline, depending on the concentration.

Lithium hydride is used to absorb carbon dioxide in space technology applications. It vigorously reacts with water to generate hydrogen and lithium hydroxide. It can produce thermal and alkaline burns.

Oxidants

Bleaches

Chlorites are the primary chemicals used as bleaches in the United States. Household bleach is alkaline with a pH of 11-12, but it is dilute enough that it is minimally irritating to the skin. More concentrated, industrial strength chlorites may be more damaging to the skin.

Peroxides

Peroxides are commonly used in hair dyes. Household-grade hydrogen peroxide (3%) produces minimal-to-no skin irritation. Concentrations of 10% may cause paresthesias and blanching of the skin. Concentrations of 35% or more will cause immediate blistering.

Chromates

Potassium dichromate and chromic acid are common industrial chemicals used in tanning, waterproofing fabrics, corrosion inhibitor, painting, and printing, and they are also used as an oxidizing agent in chemical reactions. Chromates can result in severe skin burns and subsequent systemic toxicity, including renal failure.

Manganates

Potassium permanganate is a strong oxidizing agent that is used in dilute solutions as a disinfectant or sanitizing agent. In dilute solutions, it is minimally irritating to the skin. In concentrated form or pure crystals, it can cause severe burns, ulcerations, and systemic toxicity.

Other substances

White phosphorus

This chemical is used as an incendiary in the manufacture of munitions, fireworks, and fertilizer. White phosphorus is spontaneously oxidized in air to phosphorus pentoxide, giving off a yellow flame and a dense white smoke with a garlic odor. After explosions of munitions or fireworks, small particles of phosphorus can become embedded in the skin and continue to smolder. [3]

Metals

Elemental lithium, sodium, potassium, and magnesium react violently with water, including water on the skin.

Hair coloring agents

Hair coloring agents contain persulfates and concentrated solutions of peroxides. Straightening agents may contain concentrated alkali. Chemical burns can result if these are not diluted properly or have a prolonged contact time with the scalp. Burns with various products have been reported in the literature. [4]

Airbag injuries

The rapid inflation of airbags is accomplished through the rapid decomposition of sodium azide to produce nitrogen gas. The sodium generated then reacts with potassium nitrate and silicon dioxide to produce gas. In the second step, small amounts of sodium hydroxide and sodium carbonate are generated. Airbags can produce abrasions, lacerations and contusions through the physical force of the rapid expansion. They can also produce alkaline chemical burns. These are especially concerning when corneal abrasions occur due to airbags. [5]

Vesicants

These agents are primarily chemical warfare agents and are also known as blister agents. They include sulfur and nitrogen mustards, arsenicals, and phosgene oxime. For more information see CBRNE – Vesicants, Mustard: Hd, Hn1-3, H and CBRNE – Vesicants, Organic Arsenicals: L, ED, MD, PD, HL.

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Epidemiology

Frequency

United States

Burns are a common problem seen in the emergency department. There has been a decrease in the number of burns in the United States through 2000, but this appears to have stabilized since. Most burns are only partial thickness and occur on the extremities. Approximately 5% of individuals with burns presenting to the ED require admission. [6]

In 2011, the American Association of Poison Control Centers (AAPCC) reported 15,616 cases of exposures to acidic substances, 18,960 cases of exposures to alkaline substances, 20,518 cases of peroxide exposures, and 38,613 cases of bleach exposures. During that time, 352 cases of exposure to phenols or phenol products were reported. [7] Chemical injuries account for 2-6% of burn center admissions. [3]

International

Worldwide, corrosive substances are commonly used for chemical assault. The most common substances used are lye and sulfuric acid. [8, 9, 10]

Sex

Assaults with caustic chemicals worldwide are more likely to occur against women. [8]

Age

Adults and children are nearly equally exposed to caustic chemicals. Adults exposed to industrial strength chemicals often suffer more severe burns.

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Prognosis

The prognosis depends entirely on the extent of tissue injury. Small lesions heal well, whether dermal or esophageal. Larger dermal burns can produce significant scarring. Extensive esophageal lesions can result in future stricture formation. Hydrofluoric acid burns can cause progressive tissue injury and may result in loss of digits.

Even moderate corneal burns can result in scarring and loss of vision. Sometimes this can be remedied by corneal transplantation.

Mortality/morbidity

In the 2011 report of the American Association of Poison Control Centers, exposures to acids and acid-containing products and chemicals resulted in 8 deaths, 78 cases of major toxicity, and 1270 cases of moderate toxicity. Exposures to alkali products and chemicals resulted in 4 deaths, 136 cases of major toxicity, and 1995 cases of moderate toxicity. Exposures to peroxides resulted in no deaths, 13 cases of major toxicity, and 226 cases of moderate toxicity. Exposures to bleaches and hypochlorite-containing products resulted in 22 cases of major toxicity and 968 cases of moderate toxicity. Exposures to phenol-containing products resulted in 47 cases of moderate toxicity. [7]

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Patient Education

For cases of occupational exposure, educate the patient on the proper safety precautions that should be taken when working with hazardous materials. All industries are required to inform employees of any dangerous materials they may come into contact with in the workplace and must provide them with adequate training and protective equipment.

When children experience chemical burns, counsel the parents on how to keep medications and chemicals out of the reach of children. Parents may not think that something like automatic dishwashing detergent can be a danger to children. Inform them of the various substances in the home that are potentially dangerous. Consultation with the local social services agency may be indicated to evaluate the child's home situation.

For patient education resources, visit the First Aid and Injuries Center.

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