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Chemical reactions in acid and alkali accidents

Understand the chemistry behind acid and alkali accidents. Explore how chemical reactions cause tissue damage, why alkalis can penetrate deeper, and how pH plays a role in the severity of an injury.

What happens when acids or alkali come into contact with the body?

Chemical injuries to the eyes and skin can develop rapidly and cause severe tissue damage. The extent of the injury depends on several factors, including the chemical properties of the substance, its concentration, the duration of exposure, and how quickly rinsing is initiated.

Acids and alkalis affect tissue through different chemical mechanisms. Acids primarily damage cellular proteins, whereas alkalis mainly break down the lipids in cell membranes and therefore often penetrate deeper into the tissue. Immediate and appropriate rinsing is essential to limit these chemical reactions and reduce tissue damage.

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Structure of the eye and normal pH balance

The surface of the eye, particularly the cornea, consists of several layers of living cells. Each cell is surrounded by a cell membrane composed primarily of phospholipids and proteins. The cell membrane acts as a protective barrier that regulates which substances can enter and leave the cell.

For cells to function normally, the surrounding environment must remain stable. Tear fluid normally has a pH of approximately 7.3–7.4, which is close to neutral.

Photo source: The image was generated using AI

Photo source: The image was generated using AI

Chemical reactions in the eye

Acid injuries to the eye

When an acid comes into contact with the eye, it releases hydrogen ions (H⁺), which react with proteins in the cell membranes and surrounding tissue. These hydrogen ions can alter the three-dimensional structure of proteins, causing them to lose their normal function. This process is known as protein denaturation.

As proteins denature, the cell membrane becomes less stable and more permeable. Cells may begin to lose water and ions, resulting in irritation and tissue damage.

Acid injuries are often more superficial because the proteins coagulate, forming a barrier that can partially limit further penetration of the acid into deeper tissue.

Eye damage caused by en acid:

    Photo source: The image was generated using AI

    Alkali injuries to the eye

    Alkalis release hydroxide ions (OH⁻), which primarily react with the lipids in the cell membrane. Because the membrane consists largely of phospholipids, hydroxide ions can break it down through a process similar to soap formation, known as saponification.

    As the cell membrane dissolves, cells lose their protective structure. At the same time, the tissue becomes more permeable, allowing the alkali to penetrate deeper into the cornea and other structures of the eye.

    For this reason, alkali injuries are often more severe and may progress rapidly.

    Eye damage caused by en alkali:

        Photo source: The image was generated using AI

        Injuries caused by either alkali, acids or foreign bodies

        If you are looking for a clear and practical introduction to acid and alkali accidents, including what happens when chemicals come into contact with the eyes or skin, what to do, and how the right first aid can help, you can explore the topic here:

          Eye injuri with chemicals

          Chemicals can penetrate the eye in the form of a solid, liquid or gas.

          • Acids – primarily damage cellular proteins and often not so deep in the tissue.
          • Alkalis – often cause deeper injuries with scarring as a result.

          Eye injuri with foreign body

          Many eye injuries are caused by mechanical influences, primarily foreign bodies.

          Even ‘minor’ eye injuries can cause life-long vision problems and suffering.

          Damage to the cell membrane

          At the molecular level, cells are composed of proteins, lipids, and water. Hydrogen ions released by acids can alter the structure of proteins, while hydroxide ions released by alkalis break down the lipids that make up the cell membrane.

          When this occurs, the cell loses its protective barrier, making it increasingly vulnerable to further chemical damage.

            Photo source: The image was generated using AI

            Chemical injuries to the skin

            The skin consists of several layers, including the epidermis and dermis. Like the cells of the eye, skin cells are surrounded by cell membranes composed of phospholipids and proteins.

            The surface of healthy skin normally has a pH of approximately 4.5–5.5. This slightly acidic environment, known as the acid mantle, helps protect the skin against chemical exposure and microorganisms.

              Photo source: The image was generated using AI

              Acid Injuries to the skin
              Acids primarily affect proteins within skin cells. Hydrogen ions can alter the structure of proteins, leading to denaturation and coagulation.

              As proteins coagulate, they may form a firmer layer within the tissue that partially limits further penetration of the acid. Consequently, acid injuries are often more superficial, although they can still be severe and painful.

              Alkali Injuries to the skin
              Alkalis react with the lipids in cell membranes and dissolve the membrane structure through saponification. As the cell membranes are destroyed, the tissue loses its protective barrier.

              The alkali can then penetrate deeper into the skin, continuing to break down both proteins and lipids. Consequently, alkali injuries are often deeper and more severe than acid injuries.

                Photo source: The image was generated using AI

                Osmosis and tissue damage

                When a strong acid or alkali comes into contact with the skin or eye, the tissue is affected not only chemically. Changes also occur in osmosis, ion balance, and fluid pressure at the cellular level. These processes can worsen tissue damage and influence how deeply the chemical penetrates.

                    Photo source: The image was generated using AI

                    Osmosis

                    Osmosis is the movement of water through a semipermeable membrane (such as a cell membrane) from an area with a lower concentration of dissolved substances to an area with a higher concentration.
                    The cell membrane consists of a phospholipid bilayer containing proteins, making it selectively permeable. Water can therefore move across the membrane by:

                    • Diffusion through the membrane
                    • Specialized water channels (aquaporins)

                    When chemicals alter the concentration of ions within the tissue, the osmotic balance also changes, causing water to move into or out of the cells.

                    Acid

                    When an acid contacts the skin or eye, hydrogen ions (H⁺) are released.

                    These ions can:

                    1. Alter the structure of proteins (protein denaturation)
                    2. Increase the concentration of dissolved ions within the tissue

                    The increased ion concentration creates an osmotic gradient that draws water out of the cells. This may result in cellular dehydration, damage to cell membranes, and protein coagulation.

                    In the skin, this may lead to coagulation necrosis, in which tissue proteins coagulate and form a relatively firm surface. This surface may actually limit how deeply the acid penetrates.

                    In the eye, dehydration and protein changes can damage the corneal epithelium, increase tissue density, and cause pain and inflammation.

                    Alkali

                    The effects of alkalis are often more severe. When an alkali contacts the skin or eye, hydroxide ions (OH⁻) are released and react with the lipids in cell membranes. This process is called saponification, during which membrane lipids are broken down.

                    As the cell membrane is destroyed, it becomes more permeable, allowing ions and water to move freely. This can result in cell swelling, fluid accumulation, and deeper tissue damage.

                    In the skin, alkalis may therefore cause liquefaction necrosis, in which tissue dissolves and the chemical penetrates progressively deeper.

                    In the eye, alkalis can rapidly penetrate the corneal epithelium, the corneal stroma, and in severe cases even reach the anterior chamber.

                    The increased permeability also allows osmosis to draw water into the tissue, leading to oedema (swelling).

                    The eye is particularly sensitive to changes in osmosis and pressure because its fluid balance is tightly regulated. These fluids normally have an osmolarity of approximately 300 mOsm/L.

                    When an acid or alkali enters the eye:

                    • Ion concentration changes
                    • Osmolarity changes
                    • Water begins to move between tissues and fluids

                    This may result in:

                    • Corneal oedema
                    • Changes in intraocular pressure
                    • Reduced corneal transparency

                    If corneal cells swell, light is scattered differently through the tissue, leading to blurred vision.

                    Looking for a more practical overview?

                    If you are looking for a clear and practical introduction to acid and alkali accidents, including what happens when chemicals come into contact with the eyes or skin, what to do, and how the right first aid can help, you can explore the topic here:

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