Human skin can burn, but it does not easily sustain a flame. While combustion can occur under specific, extreme conditions, its natural composition typically prevents rapid ignition.
What Human Skin Is Made Of
Human skin is primarily composed of water (55-75%), proteins, and lipids. Its high water content acts as a natural fire retardant, requiring significant energy to evaporate before other components can ignite.
Proteins (like collagen and keratin) and lipids (fats) make up the remaining dry mass. These become combustible once water is removed by intense heat. Subcutaneous tissue beneath the dermis also contains fat, which can serve as a fuel source during prolonged burning.
Conditions for Skin Ignition
Skin ignition requires extremely high temperatures and prolonged heat exposure. The flashpoint for human skin is approximately 1,600°F (871°C). Even in a burning building, temperatures can exceed this, but sustained exposure is still required for significant burning.
External accelerants significantly lower the ignition threshold and increase burning rates. Flammable liquids or gases, such as gasoline, provide additional fuel. These substances can saturate clothing or skin, bypassing the skin’s natural resistance and facilitating combustion. An external ignition source is always required; skin does not spontaneously combust.
The Burning Process of Skin
When skin burns, its high water content causes charring and dehydration before sustained flaming. Water must evaporate before proteins and lipids burn, leading to slow, smoldering combustion rather than an immediate open flame.
The extent of damage is categorized into different degrees of burns:
- First-degree burns affect only the outer layer of skin (epidermis), causing redness and pain.
- Second-degree burns involve both the epidermis and dermis, often resulting in blisters and severe pain.
- Third-degree burns are full-thickness injuries destroying all skin layers, potentially extending into underlying tissues. They may appear white, brown, or charred with little pain due to nerve damage.
- Fourth-degree burns extend through all skin layers, involving muscle, tendons, or bone.
Dispelling Myths About Skin Flammability
A common misconception is “spontaneous human combustion,” where a body supposedly bursts into flames without an external ignition source. Scientific consensus refutes this, asserting an outside heat source is always involved. Cases are often explained by the “wick effect.”
The “wick effect” theory proposes an external flame source, such as a cigarette, ignites clothing. This clothing then absorbs melted human fat, acting like a candle wick. This slow, localized burning, fueled by body fat, can extensively destroy the body while leaving surrounding areas relatively undamaged, explaining historical accounts.