Summer flu: Causes, symptoms and protection in everyday life

Especially during the summer months, flu-like symptoms occur more frequently and can be confusing in hot weather. Many people wonder whether it's a real flu, a harmless cold, or the so-called summer flu.

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What is a summer flu?

Summer flu refers to an acute, usually mild infection of the upper respiratory tract that occurs primarily in the warmer months. It is typically caused by enteroviruses, and less frequently by rhinoviruses or adenoviruses. Unlike classic winter colds, the main triggers of summer flu are not cold temperatures, but rather strong temperature fluctuations, air-conditioned environments, increased travel activity, and physical strain [3]. Despite its name, summer flu is technically not an actual “flu” in the medical sense, but a common cold.

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Difference from real flu (Influenza)

True influenza (the flu) is caused by influenza A or B viruses and tends to be much more severe than a summer cold. The typical distinguishing characteristics include [1,2]:

• Different pathogens: While summer flu is usually triggered by enteroviruses or rhinoviruses, influenza infections are caused by influenza A or B viruses.
• Onset of symptoms: Summer flu symptoms tend to appear gradually, whereas influenza often begins suddenly—within a few hours—and with a strong overall feeling of illness.
• Fever intensity: Summer flu is usually accompanied by mild or moderate fever, typically under 38.5 °C (101.3 °F). In contrast, real flu often causes high fever spikes, with temperatures above 39 °C (102.2 °F) being common.
• Symptoms: Summer flu usually causes a runny nose, sore throat, dry cough, and mild headaches or body aches. Influenza, however, typically comes with severe coughing, sudden high fever, pronounced muscle and joint pain, and a marked feeling of illness.
• Duration and course: Summer flu often resolves within a few days, while real influenza can severely affect individuals for one to two weeks and may lead to complications such as pneumonia—especially in older people or those with pre-existing health conditions.

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Typical Symptoms of Summer Flu

The most common symptoms include [1]:

• Mild to moderate sore throat
• Runny or congested nose
• Dry cough
• Headaches and body aches
• General fatigue
• Mild fever (below 38.5 °C / 101.3 °F)
• Occasionally gastrointestinal symptoms like nausea or diarrhea

Since enteroviruses can also affect the gastrointestinal tract, summer flu infections are more likely to involve digestive symptoms than a classic cold.

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When to See a Doctor

In most cases, summer flu resolves on its own within a few days without complications. However, medical consultation is recommended in the following situations:

• Fever above 39 °C (102.2 °F) or lasting more than three days
• Severe shortness of breath or persistent, intense coughing
• Very strong headaches, chest pain, or joint/muscle pain
• Signs of dehydration (e.g. due to vomiting or diarrhea)
• Belonging to a high-risk group (older adults, young children, people with chronic conditions)

If a true influenza infection or another serious illness is suspected, medical evaluation is also advised.

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Everyday Protection – Especially During Summer Holidays

Effective protection against summer flu is based on simple but powerful hygiene measures and a conscious lifestyle:

• Wash your hands regularly with soap and water, especially after using public transport or visiting swimming pools.
• Use air conditioning moderately: avoid extreme temperature differences between indoors and outdoors, as they can irritate the mucous membranes.
• Stay hydrated: drinking plenty of fluids helps keep mucous membranes moist and supports the immune system.
• Avoid direct drafts, e.g., from car air conditioners.
• Boost your immunity through a balanced diet, adequate sleep, and moderate physical activity.
• Follow cough and sneeze etiquette: cough or sneeze into your elbow or a tissue.

Especially when traveling – during long flights or in foreign climates – it’s important to pay attention to hygienic food and drinking habits to avoid infection.

Even though summer flu is usually harmless, it should not be underestimated – especially if there are risk factors or severe symptoms. Carefully distinguishing between a mild summer infection and a more serious flu can protect your health in the long term.

With simple measures like consistent hygiene, appropriate clothing, and conscious hydration, the risk of infection can be significantly reduced. Pay attention to your body during the summer holidays, listen to the signals of your immune system – and allow yourself rest at the first signs of illness.

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References

1. BR24. (2023). Lästige Sommergrippe: Ursachen, Symptome und Behandlung. https://www.br.de/nachrichten/wissen/sommergrippe-symptome-dauer-verlauf-behandlung,Thi0lvL 
2. CDC. (2024). About Influenza. https://www.cdc.gov/flu/about/index.html ‍
3. hkk-Gesundheitsredaktion. (2022). Mythos Sommergrippe?. http://dock.hkk.de/gesundheit/erkaeltung/mythos-sommergrippe