Burns: Acute Skin Barrier Loss, Systemic Inflammation, and Multiorgan Stress
Burns are injuries caused by thermal, chemical, electrical, or radiation exposure that result in partial or complete destruction of the skin barrier. Unlike most integumentary conditions, burns represent catastrophic failure of the skin as an organ, with consequences extending far beyond the site of injury.
What You Need to Know
Burns cause immediate loss of the skin’s protective and regulatory functions, exposing the body to rapid physiological instability. The skin normally limits fluid loss, maintains temperature, prevents microbial invasion, and acts as an active immune and metabolic organ. When this barrier is breached, these functions fail simultaneously, triggering changes that extend well beyond the site of injury.
The severity of burn illness is determined by the extent of skin loss and the body’s systemic response rather than depth alone. Large or partial-thickness burns provoke widespread inflammation, capillary leak, and neuroendocrine stress responses that affect cardiovascular stability, immune function, and metabolism. Even burns that appear localised can generate disproportionate systemic effects because inflammatory mediators released at the injury site circulate throughout the body.
Several early mechanisms explain why burns rapidly become a whole-body problem:
Loss of the skin barrier allows fluid, heat, and proteins to escape from the circulation
Inflammatory mediators increase capillary permeability, amplifying intravascular fluid loss
Stress hormone release drives a hypermetabolic state that increases oxygen and energy demand
As fluid shifts from the intravascular space into injured tissue and the interstitium, circulating volume falls despite visible swelling. This contributes to burn shock, characterised by reduced tissue perfusion and organ stress rather than haemorrhage. At the same time, immune defences are compromised, temperature regulation is impaired, and metabolic demands rise sharply. Burns are therefore best understood as a condition of acute barrier failure with secondary systemic inflammation, where early physiological derangement, not just tissue damage, determines outcome.
Beyond the Basics
Immediate skin barrier failure
Burn injury destroys the epidermal barrier, removing the physical and biochemical protection normally provided by intact skin. The lipid matrix and keratinocyte layers that regulate permeability are disrupted or lost, allowing uncontrolled movement of water, electrolytes, and proteins out of the body. At the same time, exposed tissue is no longer protected from microbial contamination or mechanical injury. The skin therefore shifts abruptly from a stabilising organ to a source of ongoing physiological loss.
This barrier failure explains why even relatively small surface burns can have outsized systemic effects. Transepidermal water loss begins immediately, and the body is unable to compensate through normal regulatory mechanisms. Fluid loss is continuous rather than episodic, making early instability difficult to assess by appearance alone.
Capillary leak and fluid shifts
Thermal injury activates inflammatory pathways that increase capillary permeability at the burn site and throughout the circulation. Endothelial junctions loosen, allowing plasma proteins and fluid to escape into interstitial spaces. This produces extensive oedema in burned and unburned tissue alike.
Although the body appears fluid overloaded due to swelling, effective intravascular volume falls. Circulating plasma is depleted as fluid leaves the vascular space, reducing venous return and tissue perfusion. This capillary leak state is a defining feature of early burn physiology and explains why large-volume fluid resuscitation is required despite visible oedema.
Burn shock and impaired perfusion
Burn shock results from the combined effects of intravascular fluid loss, reduced cardiac output, and systemic vasodilation. As circulating volume falls, oxygen delivery to tissues becomes inadequate, forcing cells into hypoxic metabolism. Cardiac performance may be further impaired by inflammatory mediators and electrolyte disturbances.
This form of shock is not caused by bleeding but by vascular dysfunction and fluid redistribution. Without prompt resuscitation, reduced perfusion compromises organ function, increasing the risk of acute kidney injury, gut ischaemia, and myocardial stress. The severity of shock correlates more closely with burn surface area than with depth alone.
Hyperinflammatory response
Burns provoke a powerful systemic inflammatory response characterised by widespread release of cytokines, prostaglandins, and stress hormones. These mediators amplify capillary leak, alter vascular tone, and activate immune cells. Initially protective, this response can become excessive and self-sustaining. The hyperinflammatory state contributes to fever, tachycardia, insulin resistance, and altered immune signalling. In severe burns, inflammation extends beyond local defence and begins to drive organ dysfunction, illustrating how immune activation becomes maladaptive rather than restorative.
Hypermetabolic state
After the initial shock phase, burn patients enter a prolonged hypermetabolic state driven by stress hormones and inflammatory mediators. Resting energy expenditure rises markedly as the body attempts to repair tissue, maintain temperature, and support immune activity.
Protein breakdown accelerates to supply amino acids for wound healing and acute-phase responses. This catabolic state leads to muscle wasting, weakness, and impaired immunity if nutritional demands are not met. The hypermetabolic response explains why recovery from burns is prolonged and why aggressive nutritional support is essential.
Immune suppression and infection risk
Despite intense inflammation, burn injury results in impaired immune defence. Loss of skin integrity removes a primary barrier to infection, while systemic immune responses become disorganised and less effective. Neutrophil function, antigen presentation, and cell-mediated immunity are all reduced.
Burn wounds provide a warm, protein-rich environment that supports microbial growth. Combined with immune dysfunction, this makes infection and sepsis major contributors to morbidity and mortality following burns, even when initial resuscitation is successful.
Thermoregulatory failure
The skin plays a critical role in temperature regulation through control of heat loss and conservation. Burn injury disrupts vasomotor control and evaporative regulation, impairing the body’s ability to maintain thermal stability.Patients are vulnerable to hypothermia early due to heat loss and fluid evaporation, and to fever later as inflammation and infection develop. Temperature instability reflects loss of normal skin function rather than environmental exposure alone.
Delayed wound healing and scar formation
Effective wound healing requires viable tissue, adequate perfusion, and resolution of inflammation. Extensive burns limit epithelial migration and prolong the inflammatory phase of repair. As healing progresses, fibroblast activity and collagen deposition may become excessive.
This process leads to hypertrophic scarring and contracture formation, particularly across joints and mobile surfaces. These long-term structural changes can significantly impair movement and function, demonstrating that burn injury continues to exert physiological and mechanical consequences long after the acute phase has resolved.
Clinical Connections
Burns may present with obvious local features such as pain, blistering, skin loss, or charring, but the severity of illness is often driven by systemic responses rather than wound appearance. Early deterioration can occur even when burns seem limited, reflecting rapid fluid shifts, capillary leak, and inflammatory mediator release. Airway compromise may develop from inhalation injury or oedema, circulation may be threatened by intravascular volume loss, and temperature instability can appear early due to loss of skin-mediated regulation.
Several early priorities are dictated by the underlying physiology rather than the visible injury:
Airway protection in anticipation of oedema and inhalation-related inflammation
Aggressive fluid resuscitation to counter capillary leak and intravascular depletion
Temperature control to reduce heat loss and metabolic stress
Infection prevention due to immediate loss of the skin’s immune barrier
Clinical management therefore focuses first on stabilising physiological systems before definitive wound care. Pain control, monitoring of organ perfusion, and early nutritional support are also essential because metabolic demand rises quickly after injury. Delaying systemic support while focusing on wound appearance alone risks progression to shock, organ dysfunction, or infection. Burns must be approached as a systemic inflammatory illness that originates in the skin, where early intervention targets whole-body stability to prevent downstream complications rather than treating the burn as an isolated local injury.
Concept Check
Why does skin barrier loss cause rapid fluid imbalance after burns?
How does capillary leak contribute to burn shock?
Why do burn patients develop a hypermetabolic state?
How can severe inflammation coexist with immune suppression?
Why are infection and organ dysfunction major late complications of burns?