What kills you when struck by lightning?

[FinnFitz]

The primary cause of death from a lightning strike is immediate cardiac arrest, triggered by the massive electrical current disrupting the heart's rhythm. The second major killer is respiratory arrest from brainstem paralysis. While external burns may be minor, catastrophic internal injuries—including tissue destruction, organ damage, and neurological trauma—often prove fatal. Survival hinges on immediate CPR, as the heart's paralysis is often temporary but the window for revival is critically short.

The lethality stems from lightning's extreme power: a bolt can carry up to 100 million volts and temperatures five times hotter than the sun's surface. This energy doesn’t just travel over the skin; it passes through the body’s cardiovascular and nervous systems, causing systemic failure.

The specific fatal mechanisms are:

Mechanism	Physiological Impact	Result
Cardiac Arrest	The massive current overrides the heart's natural electrical system, causing ventricular fibrillation or asystole (complete stop).	Heart ceases to pump blood; death within minutes without intervention.
Respiratory Arrest	The current paralyses the brain's medullary respiratory center, which controls breathing.	Breathing stops, leading to fatal oxygen deprivation.
Neurological Damage	Direct electrical injury to the brain and nervous system can cause instant brain hemorrhages, seizures, or coma.	Can be immediately fatal or cause severe, permanent disability.
Internal Thermal & Blast Injuries	The current causes rapid, violent heating of tissues and bodily fluids, leading to deep burns, organ rupture, and vascular damage.	Massive internal injury leads to shock and multi-organ failure.

Contrary to common belief, the "flashover" effect—where current travels over the skin—can sometimes increase survival chances by reducing internal current. However, if the energy penetrates internally, the damage is severe.

The pathway of the strike also determines risk. A direct strike (part of the main channel) is most lethal. However, ground current—where lightning hits the ground and spreads outward—is the most common killer, especially for animals and people with their feet apart. Side flashes (from a nearby object) and conduction (through wires or pipes) are also dangerous.

Market data from wilderness medicine studies indicates that about 10% of lightning strike incidents are fatal. For the 90% who survive, many suffer long-term neurological, sensory, and psychological sequelae. The critical takeaway is that rapid CPR and defibrillation are vital, as the heart is often in a "stunned," reversible state rather than permanently damaged.

[DelGrace]

As a backpacking guide for over 20 years in the Rockies, I’ve seen my share of close calls. Here’s the brutal truth: lightning doesn’t need a direct hit to kill you. The ground current is the real silent killer. I tell my groups, if your hair stands on end or you hear crackling, the charge is building—crouch low on your gear, feet together, NOW. It’s about minimizing the voltage difference between your contact points. The bolt itself stops your heart or breathing. We’re trained that if someone gets hit, start CPR immediately and don’t stop. Their heart might just be in a temporary electrical shock and can restart. Hesitation is what seals the deal.

[MacJustin]

I work in an emergency department, and we approach lightning injuries as a massive multisystem trauma. The instant cause of death is typically cardiopulmonary arrest—the jolt acts like defibrillating the entire body at once, but chaotically. What people don’t see are the internal burns. The current follows blood vessels and nerves, cooking them from the inside. This can rupture organs, cause muscle tissue to break down (rhabdomyolysis), and flood the kidneys. Neurologically, patients can have immediate brain swelling or hemorrhages. The key for bystanders is to act fast: the victim is safe to touch. Begin chest compressions. Their heart rhythm might be recoverable, but their brain can’t last long without oxygen.

[McRachel]

I was struck. It felt like a bomb went off inside my head. There was no pain at first, just an overwhelming force and then nothing. I woke up later with people around me. The doctors told me I survived because my heart basically just “rebooted” itself, but my nervous system took the hit. For years after, I had memory lapses, constant ringing in my ears, and debilitating fatigue. The physical scars were minor. The real damage was invisible—the neurological storm that the lightning started in my brain and never fully stopped. Death from lightning isn’t always on the spot; it can be a cascade of system failures, or a life profoundly altered by the internal damage.

[DiRhett]

Most lightning fatalities are preventable. The mechanics are clear: the electrical discharge seeks the path of least resistance to the ground. When it travels through a human body, it disrupts our bioelectrical systems. The heart’s rhythmic pumping relies on precise electrical impulses; a lightning bolt overwhelms this circuit. Simultaneously, the brainstem—our breathing control center—short-circuits. This one-two punch of cardiac and respiratory arrest is what causes death within minutes. Immediate, high-quality CPR is the only effective countermeasure, manually circulating blood and oxygen until professional help arrives. Understanding this sequence underscores why seeking shelter before the storm arrives is non-negotiable. There is no safe place outdoors during a thunderstorm.