The potential for a chemical substance to destroy human tissue is directly related to its concentration of hydrogen ions, quantified by the pH scale. This scale ranges from 0 to 14, with 7 representing a neutral substance, such as pure water. Values below 7 indicate increasing acidity, while values above 7 signify increasing alkalinity (basicity). The scale is logarithmic, meaning each whole number change represents a tenfold difference in acidity or alkalinity. Corrosion refers to the irreversible chemical destruction or severe damage to living tissue upon contact. Exposure to substances at the extreme ends of this scale can result in severe chemical burns.
The Skin’s Protective Barrier: The Acid Mantle
The surface of human skin operates within a narrow, slightly acidic range. This protective layer, known as the acid mantle, maintains a pH between 4.5 and 5.5, sustained by a mixture of sweat, sebum, and amino acids.
The acid mantle serves as a first line of defense against environmental threats and pathogenic microorganisms. Its low pH environment inhibits the growth of many harmful bacteria and fungi. This slightly acidic state is also integral to maintaining the skin’s barrier function, regulating moisture retention and integrity.
When the skin encounters a substance with a pH that deviates significantly from this optimal range, the acid mantle’s protective function is compromised. Exposure to chemicals outside the 4.5 to 5.5 range can weaken the skin’s defense system. This disruption increases the skin’s susceptibility to irritation and severe chemical injury.
Defining Corrosive pH Ranges
A substance is classified as corrosive to human tissue based on its capacity to cause visible destruction, indicated by its pH value. A substance is considered immediately corrosive if its pH falls at or below 2.0 or at or above 11.5. These extreme values signify the concentration of hydrogen or hydroxide ions sufficient to rapidly break down biological structures.
Highly acidic solutions (pH 2.0 or lower) contain an overwhelming concentration of free hydrogen ions. Strong acids, such as concentrated hydrochloric acid, cause severe tissue damage upon contact. Highly alkaline substances (pH 11.5 or greater), such as lye or concentrated bleach, are also corrosive. These powerful bases are often considered more dangerous because they penetrate deeper into the skin layers.
Corrosive potential is not solely determined by the pH number. The concentration of the chemical and the duration of contact are equally important factors in determining burn severity. Substances slightly outside the corrosive threshold (e.g., pH 3 or pH 11) can still cause significant damage if exposure is prolonged. The substance’s acid or alkaline reserve also influences how long it maintains its destructive pH despite dilution by tissue fluid.
Chemical Mechanisms of Skin Damage
Acids and alkalis destroy tissue through different chemical processes, resulting in different types of burns. Acidic substances cause coagulation necrosis when the acid reacts with proteins in the skin, causing them to denature and solidify.
The resulting solid, leathery layer is called an eschar, and its formation physically limits the acid’s ability to travel deeper into the underlying tissue. While the initial surface damage is severe, this coagulum acts as a temporary barrier, often keeping the burn more superficial. Hydrofluoric acid is an exception, behaving more like an alkali and causing a deeper burn despite its low pH.
Alkaline substances, or bases, cause liquefaction necrosis. Bases react with fats in cell membranes through saponification. Simultaneously, the alkali breaks down structural proteins, destroying the tissue’s integrity rather than solidifying it. Because this reaction does not create a protective barrier, the chemical penetrates rapidly and deeply, leading to extensive destruction of the underlying tissue.
Immediate Action Following Exposure
Immediate first aid following a chemical burn is the most important factor in limiting tissue damage. The first step is to remove the chemical from the skin as quickly as possible by immediately flushing the affected area with cool, running water.
The area should be flushed continuously for a minimum of 20 minutes to ensure the chemical is diluted and washed away. While flushing, all contaminated clothing and jewelry must be removed to prevent prolonged contact. If the substance is a dry chemical or powder, it must be brushed off the skin before water is applied, as water can sometimes intensify the corrosive reaction.
Once flushing is complete, the burn area should be loosely covered with a clean, dry, sterile dressing. Do not apply any neutralizing agents, creams, or ointments, as these can generate heat and worsen the injury. Even if the burn appears minor, immediate medical attention must be sought for a professional assessment of the injury depth and severity.