June 28, 2026, 10:29 am | Read time: 5 minutes
The transition from sunstroke to heatstroke is often gradual. In the worst case, heatstroke can lead to death. A neurologist explains what exactly happens in the body during these two heat emergencies and what the symptoms are.
Sunstroke and Heatstroke – Here’s the Difference
In both cases, high temperatures cause damage. Prof. Dr. med. Frank Erbguth, president of the German Brain Foundation, explains the difference between sunstroke and heatstroke to FITBOOK as follows: “Simply put, sunstroke affects ‘only’ the head, meaning the brain. The rest of the body is fine. In contrast, with heatstroke, the body’s entire temperature regulation collapses.”
When Sunstroke Occurs and Who Is Particularly at Risk
Sunstroke can occur when the head and neck area have been exposed to too much sun. The intense heat irritates the brain and meninges, Erbguth tells FITBOOK. “The brain is not the most robust organ. During sunstroke, the meninges and brain warm up.” Just one to two degrees Celsius is enough to produce a type of meningitis.
Those particularly at risk are people with no, little, or very thin hair. This includes older adults, as well as toddlers and babies. Infants, for example, have only a thin skull.
Signs of Sunstroke
Sunstroke is indicated by headaches and dizziness. But also neck pain and stiffness, light sensitivity, and a bright red, hot head can suggest sunstroke.1 According to the German Red Cross, symptoms may also appear only after being out of the sun for several hours.
Overview of Sunstroke Symptoms
- Headaches
- Dizziness
- Neck pain, neck stiffness
- Light sensitivity
- Bright red, hot head
- High fever in young children
What to Do if Sunstroke Is Suspected
If sunstroke is suspected, the affected person should be removed from the heat and taken to a cool place. There, the body should be cooled with wet cloths, with the upper body ideally elevated. Additionally, the affected person should drink plenty of fluids.
If the condition worsens and consciousness fades, professional help should be requested by calling 112.
Preventing Sunstroke
To prevent sunstroke, the Johanniter-Unfall-Hilfe recommends wearing a hat, preferably a sun hat with a brim. This is especially important for people with little hair, such as infants, children, and those with thinning hair or baldness.2 The midday sun should be completely avoided. Additionally, one should drink two to three liters of water daily, wear airy, light clothing made of linen or cotton, and avoid alcohol in the sun.
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When Heatstroke Threatens
Prof. Erbguth explains to FITBOOK what happens in the body during heatstroke: “Our body temperature is normally 37 degrees. Heatwaves, where even the nights don’t bring cooling, can severely stress the body. At a certain point, it can no longer cool down through sweating, especially if you don’t drink enough.”
Heatstroke can also occur if one is exposed to extreme heat and humidity and cannot sweat, such as in unventilated rooms or insulating clothing. The heat essentially builds up in the body and cannot escape. During heatstroke, the body can no longer cool down through sweating—even if enough fluids have been consumed.
If the body can no longer transport the heat away, “a heat buildup occurs, and the body temperature rises to 40 degrees and higher,” explains Erbguth. This has drastic consequences for various systems in the body.
Heatstroke: In the Worst Case, Multiorgan Failure Threatens
Erbguth: “First, the coagulation and circulation systems fail. Then the blood clots. The small clots block the small vessels. The kidneys, as well as the liver and heart, can no longer function properly.”
In heat, our blood vessels widen so that as much overheated blood as possible is transported to the skin. There, the heat can be released through sweating—as sweat evaporates on our skin, the skin is cooled—and thus the blood is cooled. It can then travel to other areas of our body. “In heatstroke, this system fails. In the worst case, multiorgan failure threatens,” says Erbguth.
Sunburns in Children? Far from Rare
Possible symptoms of encephalitis
Signs of Heatstroke
Signs of heatstroke include sudden fatigue, headaches, and a vague feeling of dizziness. “If it gets worse, nausea and vomiting occur. And then: unconsciousness,” explains Erbguth.
Overview of Heatstroke Signs
- Sudden fatigue
- Headaches
- Vague feeling of dizziness
- If it gets worse, nausea, vomiting, and unconsciousness occur
If heatstroke is suspected, immediately call emergency services at 112! If someone shows the described signs, bystanders should immediately inform emergency services. Heatstroke can lead to coma and, in the worst case, be fatal. Therefore, suspicion of heatstroke is always a case for emergency services at 112.
Heatstroke: How to Properly Cool the Affected Until the Paramedics Arrive
- Until medical professionals arrive, the affected person should be immediately brought into the shade. Then the body must be cooled down—but not with pure ice on bare skin. Frostbite is a risk here, warns Erbguth. It’s better to wrap ice cubes and cold packs in a cloth.
- If the affected person is still conscious, offer them something to drink: water, juice spritzers, and fruit teas are suitable.
- Paramedics then provide cooling infusions to the affected. If the coagulation system is already disturbed, anticoagulant medications are administered in the hospital.
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Humid or Dry Heat – Which Is Worse for the Body?
With relatively high humidity, our body cools down less effectively through sweating than with low humidity. Erbguth offers this rule of thumb: “Humid heat is significantly worse than dry heat.”