Heat-Related Illnesses

Why This Matters

Heat-related illnesses exist on a severity spectrum, and your ability to recognize where someone falls on that spectrum determines whether you're dealing with a minor inconvenience or a life-threatening emergency. You're being tested on your understanding of thermoregulation, fluid-electrolyte balance, and cardiovascular response to heat stress—not just memorizing symptoms. The key distinction you must master is identifying when the body's cooling mechanisms are still working (and just need support) versus when they've completely failed (requiring emergency intervention).

Don't just memorize that heat stroke involves high temperature—understand why confusion signals a medical emergency, how the progression from cramps to exhaustion to stroke occurs, and what interventions match each stage. When you can explain the underlying physiology, you'll never confuse these conditions on an exam or in a real emergency.

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Conditions Where Cooling Mechanisms Still Function

These conditions occur when the body is struggling but still actively trying to cool itself. Sweating continues, blood vessels dilate, and the thermoregulatory system remains online—it just needs help catching up.

Heat Cramps

• Electrolyte depletion causes involuntary muscle spasms—typically in legs, arms, or abdomen during or after intense exertion in heat
• Sweating is still present, indicating the body's cooling system works; the problem is mineral loss (sodium, potassium) from that sweating
• First aid focuses on replacement: move to cool area, provide electrolyte drinks (not just water), and gently stretch affected muscles

Heat Exhaustion

• Heavy sweating with systemic symptoms—weakness, dizziness, nausea, headache, and cool/clammy skin signal the body is losing the thermoregulation battle
• Core temperature elevated but below $104°F$ ($40°C$); mental status remains intact, which distinguishes this from heat stroke
• Aggressive cooling required: move to cool environment, remove excess clothing, apply cool wet cloths, and hydrate with water or sports drinks

Heat Syncope (Fainting)

• Blood pooling in legs causes fainting—prolonged standing or sudden position changes in heat reduce blood return to the heart and brain
• Vasodilation is the culprit: blood vessels expand to release heat, but this drops blood pressure when combined with gravity
• Position is your intervention: lay person flat in cool area, elevate legs above heart level, and provide fluids once conscious

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Conditions Where Cooling Mechanisms Have Failed

This is the emergency category. The hypothalamus can no longer regulate temperature, sweating stops, and core temperature rises uncontrolled. Recognizing this failure point is the most critical skill in heat illness assessment.

Heat Stroke

• Body temperature $≥104°F$ ($40°C$) with altered mental status—confusion, slurred speech, seizures, or unconsciousness indicate brain dysfunction from overheating
• Skin is hot and often dry (sweating has stopped); this signals complete thermoregulatory failure and distinguishes stroke from exhaustion
• This is a medical emergency: call 911 immediately, cool aggressively with ice packs to neck/armpits/groin, immerse in cold water if possible, and monitor airway until help arrives

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Skin-Level Responses to Heat

Not all heat conditions are systemic. When sweat ducts become blocked, local inflammation occurs without threatening core temperature regulation.

Heat Rash

• Blocked sweat ducts cause red, itchy bumps or blisters—typically in areas where skin folds or clothing traps moisture
• Not a thermoregulatory emergency; the body can still cool itself, but localized skin irritation causes discomfort
• Keep skin cool and dry: move to air-conditioned space, wear loose clothing, apply calamine lotion or hydrocortisone for itching

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Quick Reference Table

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Self-Check Questions

1. A person has been working outside, is sweating heavily, and complains of dizziness and nausea but answers your questions clearly. Is this heat exhaustion or heat stroke, and what's the key indicator?

2. Compare heat cramps and heat exhaustion: what do they share in terms of the body's cooling status, and what distinguishes their primary cause?

3. Why does the presence or absence of sweating matter when distinguishing heat exhaustion from heat stroke?

4. A runner collapses after standing at the finish line on a hot day but regains consciousness quickly when laid flat. Which condition is this most likely, and what physiological mechanism caused it?

5. If an FRQ asks you to explain the progression of heat illness from mild to severe, what three conditions would you describe in order, and what changes at each stage?