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 be fatal. A medical expert explains what exactly happens in the body during these two heat emergencies and what the respective symptoms are.
Sunstroke and Heatstroke–This Is the Difference
In both cases, high temperatures cause damage. The difference between sunstroke and heatstroke is explained by Prof. Dr. med. Frank Erbguth, president of the German Brain Foundation, to FITBOOK as follows: “Simply put, with sunstroke, ‘only’ the head is affected, meaning the brain. The rest of the body is fine. In contrast, with heatstroke, the entire body’s 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. In sunstroke, the meninges and brain warm up.” Just one to two degrees Celsius is enough to produce a type of meningitis.
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 skullcap.
Signs of Sunstroke
Sunstroke manifests through headaches and dizziness. But neck pain and stiffness, light sensitivity, and a bright red, hot head can also indicate 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
- In young children: high fever
What to Do if Sunstroke Is Suspected
If sunstroke is suspected, the rule is: Get the affected person out of the heat and 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 called at 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.
Also interesting: Cold or warm water–which is healthier to drink?
When Heatstroke Threatens
What happens in the body during heatstroke is explained by Prof. Erbguth to FITBOOK: “Our body temperature is normally 37 degrees. Heatwaves, where even the nights bring no relief, can heavily burden the body. At a certain point, it can no longer cool down through sweating, especially if you don’t drink enough.”
Heatstroke also threatens when exposed to extreme heat and humidity without the ability to sweat, such as in unventilated rooms or insulating clothing. The heat essentially builds up in the body and cannot escape. In heatstroke, the body can no longer cool down through sweating–even if you have drunk enough.
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. Kidneys, as well as the liver and heart, can no longer function properly.”
In heat, our blood vessels dilate 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 as well. It can then travel cooled to other areas of our body. “In heatstroke, this system fails. In the worst case, multiorgan failure threatens,” says Erbguth.
Why Cold Drinks Can Be the Better Choice in Extreme Heat
Sunburns in Children? Far from Rare
Signs of Heatstroke
Signs of heatstroke include sudden fatigue, headaches, and a diffuse feeling of dizziness. “If it gets worse, nausea and vomiting occur. And then: unconsciousness,” explains Erbguth.
Overview of Heatstroke Signs
- Sudden fatigue
- Headaches
- Diffuse 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 a 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, they should be offered something to drink: water, juice spritzers, and fruit teas are suitable.
- Paramedics then provide the affected with cooling infusions, for example. If the coagulation system is already disturbed, anticoagulant medications are administered in the hospital.
Also interesting: What to do in case of a wasp sting
Humid or Dry Heat–Which Is Worse for the Body?
In relatively high humidity, our body cools down less effectively through sweating than in low humidity. Erbguth offers this rule of thumb: “Humid heat is significantly worse than dry heat.”