A thermal injury occurs when the body’s tissues sustain damage from the transfer of energy, resulting in the destruction of cells and proteins within the skin and underlying structures. This damage is typically caused by extreme heat sources, such as open flames, hot liquids, or highly heated surfaces. Injuries from electricity, chemical agents, or excessive friction are also considered thermal injuries due to the resulting heat-induced tissue destruction. The severity depends on the temperature of the source and the duration of contact, which determines the ultimate depth of tissue penetration.
Classifying the Depth of Injury
The depth of the damage is the most important factor in determining a thermal injury’s prognosis and treatment plan. Burns are categorized into degrees corresponding to the specific layers of skin and tissue affected, starting with the outermost layer, the epidermis.
A first-degree burn is the most superficial type, damaging only the epidermis. These injuries are characterized by redness, pain, and warmth, but they do not blister and the skin remains intact. A mild sunburn is a common example, which typically heals quickly without scarring.
Second-degree, or partial-thickness, burns extend through the epidermis and into the underlying dermis. These injuries appear red, swollen, and moist, and are recognized by the formation of blisters. Second-degree burns are often the most painful because the nerve endings in the dermis are exposed but not destroyed.
The partial-thickness category is divided into superficial and deep injuries. Superficial partial-thickness burns involve only the upper dermis and heal spontaneously within one to three weeks. Deep partial-thickness injuries reach the lower dermis, leading to longer healing times and a higher likelihood of scarring.
Third-degree burns are classified as full-thickness injuries because they destroy the entire epidermis and dermis. The injury may also extend into the subcutaneous fat layer. These wounds often appear waxy white, leathery brown, or charred black, and they do not blanch when pressed. Paradoxically, third-degree burns are often painless in the center because the nerve endings have been completely destroyed.
The most severe injuries are sometimes classified as fourth-degree burns. This damage extends past the fat layer into underlying structures, involving muscle, tendon, or even bone. These extensive injuries require complex reconstruction and often result in prolonged disability.
Immediate Emergency Response
Immediate care after a thermal injury significantly influences the final outcome and reduces the extent of the wound. The initial response must prioritize removing the victim from the heat source to stop the damaging process. This involves extinguishing flames, flushing chemical irritants, or removing heat-retaining clothing, unless the fabric is stuck to the skin.
For minor burns, immediately apply cool, clean running water for up to 20 minutes. This cooling action provides pain relief and helps limit the spread of tissue damage. Use cool or tepid water, not ice, as extreme cold can cause intense vasoconstriction, leading to further tissue injury or hypothermia in large burns.
Once cooled, the area should be gently covered with a clean, dry cloth or sterile dressing to protect the wound and minimize pain. Avoid home remedies like butter, ointments, or grease, as these can trap heat and increase infection risk. Removing any jewelry or tight clothing is also important, as the tissue will swell rapidly.
Professional medical attention is necessary if the burn is larger than the victim’s hand size, involves the face, hands, feet, or genital area, or covers a major joint. Any third-degree burn, or one caused by chemicals or electricity, requires immediate emergency services. Other criteria for seeking help include signs of infection or a burn that does not show signs of healing within two weeks.
The Body’s Biological Reaction and Recovery
A significant thermal injury triggers a complex systemic response affecting nearly every organ system, moving beyond the localized wound. When burns cover more than 20% of the total body surface area, the body initiates a massive inflammatory cascade. The release of inflammatory mediators and stress hormones leads to a state of hypoperfusion and organ hypofunction.
The initial systemic event is hemodynamic instability, often resulting in burn shock. The inflammatory response breaks down vascular integrity, causing a massive shift of fluid and protein from the bloodstream into the interstitial spaces. This profound fluid leak results in severe tissue swelling (edema) and a dramatic decrease in blood volume, which can suppress cardiac function.
This early phase is followed by a hypermetabolic flow phase that can persist for months or years. During this period, the body maintains an elevated metabolic rate, characterized by increased heart rate, elevated body temperature, and the breakdown of muscle protein and fat. This sustained catabolic state can lead to muscle wasting, impaired wound healing, and a heightened risk of infection.
The destruction of the skin, which acts as the primary protective barrier, leaves underlying tissues vulnerable to pathogens. The burn wound is susceptible to bacterial colonization, and the systemic inflammatory response can lead to immunosuppression. This further increases the risk of life-threatening infections and sepsis.
Tissue repair begins with inflammation, followed by proliferation where new granulation tissue fills the wound bed. The final stage is maturation, where new collagen fibers reorganize and strengthen. Deep burns requiring prolonged healing often result in scarring, such as hypertrophic scars or keloids, due to excessive collagen production.