10 Symptoms of Heat Exhaustion You Should Know

Symptoms of heat exhaustion develop when your body overheats, typically due to prolonged heat exposure or excessive physical activity. By recognizing signs of heat exhaustion, you can take steps to cool your body or seek medical attention if symptoms persist or worsen.

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1. Excessive Sweating

Heat exhaustion occurs when the body’s core temperature rises to between 98.6 F and 104 F. When core temperature rises, the hypothalamus (the part of the brain that regulates body temperature) activates your sweat glands to cool your body down.

Profuse sweating may continue even when you stop exercising or remove yourself from the heat.

2. Cool, Clammy Skin

Whenever the body is overheated, the hypothalamus will trigger the normal dilation (widening) of blood vessels near the surface of the skin, causing the skin temperature to rise. As sweat evaporates from the skin, it takes heat with it, cooling the body.

However, with heat exhaustion, sweat doesn’t evaporate as effectively, causing the skin to feel cool and clammy. If excessive fluids are lost due to sweating, the body will try to conserve fluid by reducing blood flow to the skin, causing it to feel even cooler and clammier.

3. Dull, Throbbing Headache

Excessive sweating can lead to dehydration, characterized by the loss of fluid and electrolytes (such as sodium and potassium). Blood vessels in the brain constrict to conserve fluids, causing dull, throbbing headache pain, typically in the front or back of the head.

Low sodium levels (hyponatremia) and low potassium levels (hypokalemia) can both disrupt the flow of blood to the brain, contributing to headaches.

4. Rapid, Weak Pulse

The dilation of blood vessels near the surface of the skin forces the heart to pump faster to meet the body’s increased circulatory needs. This can raise the heart rate to 120 beats per minute (bpm) or more.

Dehydration reduces the overall volume of blood. This, in turn, reduces the blood pressure, leading to a weaker pulse even as the heart beats faster to compensate for the reduced volumes.

5. Weakness and Fatigue

Heat exhaustion commonly manifests with weakness and fatigue. This occurs, in part, when the flow of blood is redirected to the surface of the skin, reducing the amount of blood and oxygen delivered to muscles and the brain.

Dehydration can increase the workload of the heart, leading to fatigue as the heart muscle itself becomes tired. Loss of electrolytes like calcium and sodium, essential for muscle function, can also cause muscles to fatigue more easily.

6. Fast and Shallow Breathing

With heat exhaustion, the increased rate of circulation forces the respiratory (breathing) rate to also increase to meet the body’s oxygen needs. But, even at a high rate, the body’s ability to cool itself may still be impaired, forcing the lungs to work even harder as energy reserves are depleted.

To help conserve energy, breathing will typically become rapid and shallow (tachypnea). This can further complicate symptoms as the shallow breathing may not adequately oxygenate the blood.

7. Dizziness and Lightheadedness

Dizziness and lightheadedness are common symptoms of heat exhaustion, caused when the dilation of blood vessels triggers a rapid drop in blood pressure (hypotension). Hypotension, in turn, reduces the amount of oxygen delivered to the brain, disrupting the body’s balance system.

These symptoms may be intensified when standing or rising from a chair, referred to as orthostatic hypotension. The force of gravity makes it even harder for the heart to pump blood from the lower body to the brain, leading to dizziness, lightheadedness, and blurred vision.

Dehydration can further complicate symptoms by reducing overall blood volumes.

8. Muscle Cramps

Muscle cramps occur due to electrolyte loss, particularly sodium and potassium, which play a crucial role in the transmission of nerve impulses that control voluntary muscle contractions.

The initial loss of sodium and potassium from dehydration can trigger twitches and spasms, which progressively worsen as more water and electrolytes are lost. The cramps themselves are often described as painful, occurring in brief, irregular bursts.

9. Irritability and Agitation

Exposure to extreme heat stimulates the release of a stress hormone called cortisol. Sudden elevations in cortisol can cause a steep drop in serotonin, which helps regulate moods, leading to sudden mood changes, agitation, and irritability.

Fatigue and sweating can also cause general feelings of unwellness (malaise). This can manifest in anxiety, causing excitability and outbursts.

10. Nausea and Vomiting

Nausea and vomiting are also common with heat exhaustion, triggered by a combination of possible factors:

• Rerouting of blood to the skin reduces the amount sent to the stomach and intestine, slowing digestion and triggering feelings of nausea.
• The activation of the hypothalamus can also overstimulate a nearby brainstem, which is involved in both gut motility (movement) and the vomiting reflex.
• Dehydration and electrolyte imbalances can also disrupt digestive processes, causing nausea and vomiting.

What to Do for Symptoms of Heat Exhaustion

If you feel symptoms of heat exhaustion:

• Stop exercise, work, and other physical activity.
• Seek shade or a cool place.
• If possible, lie down with your feet raised.
• Cool the skin with cold, wet cloths and use a fan, if available.
• Take sips of water or a sports drink if you are not vomiting.

Key Takeaways

• In heat exhaustion, the rise in body temperature can produce many adverse symptoms as the body tries to cool itself.
• Symptoms include excessive sweating, clammy skin, headache, rapid pulse, rapid breathing, weakness, nausea, lightheadedness, and mood changes.
• When you feel symptoms of heat exhaustion, stop activity, seek a cool place to lie down with your feet elevated, and cool the skin with cold, wet cloths.