November 12, 2026, 4:41 pm | Read time: 5 minutes
Viral infections are extremely common: 80 to 90 percent of respiratory illnesses are of viral origin. However, it’s not always clear if a virus is actually causing the symptoms. FITBOOK explains what happens in the body during a viral infection, how to recognize it, and what can help alleviate the symptoms.
A viral infection occurs when viruses enter the body and infect suitable cells. However, not every contact with a virus and not every infection automatically leads to symptoms. Whether and how severely we become ill depends, among other things, on the specific virus, the affected cells, and the immune system’s response. Another issue is that viral and bacterial infections can cause similar symptoms, making them difficult to distinguish from each other.
Why distinguishing between viruses and bacteria is important
Whether viruses or bacteria are behind an infection makes a crucial difference. Yet, both pathogens are often lumped together in everyday life. This is partly because the symptoms can be very similar. Fever, cough, sore throat, headache, body aches, and fatigue are possible with both. This significant overlap makes it difficult even for experts to determine the pathogen based solely on symptoms.
An accurate diagnosis is essential for choosing the right therapy. While bacterial infections can be treated with antibiotics, these are completely ineffective against viral diseases.1 Antibiotics are often prescribed even when a bacterial cause is not confirmed. According to the German Society for Infectious Diseases, about one-third of antibiotic prescriptions are unnecessary, too long, or incorrect.2
Can you diagnose a viral infection yourself?
As mentioned earlier, a reliable diagnosis based solely on symptoms is not possible. Therefore, laypeople cannot confidently determine if a virus is causing the symptoms. Do not rely on common myths, such as the color of nasal mucus indicating whether viruses or bacteria are involved.
Why self-diagnosis is useless
Googling symptoms or consulting chatbot AIs offers little practical benefit when suspecting a viral infection. Even if your assumption is correct, it doesn’t change the home measures.3 There is no causal therapy for most viruses, so only symptom relief is possible.
Unlike many bacterial infections, there is no specific medication for many common viral diseases. In the case of uncomplicated viral infections, the immune system usually does the main work. You can support your body by alleviating fever, pain, or a stuffy nose.4
What you can do about the symptoms
Physical rest and adequate hydration can support the body during recovery. Depending on the symptoms, over-the-counter remedies such as acetaminophen or ibuprofen for pain and fever may be considered. Saline solutions or short-term decongestant nasal drops can provide relief for a stuffy nose; for a sore throat, gargling or appropriate pharmacy remedies can help.
How long does a viral infection last?
The duration and course depend, among other things, on the type of virus involved and how the immune system responds. An uncomplicated viral respiratory infection often resolves within three to seven days. However, individual symptoms such as dry cough, hoarseness, or fatigue can persist for up to two weeks or even longer. Recovery from more severe viral infections like the flu or COVID-19 can also take longer. Some viruses can remain in the body for years or permanently, such as HIV or chronic hepatitis B and C.
Diagnosis
The symptom overlap in bacterial and viral infections means that multiple tests are needed for a reliable distinction. Doctors first consider the symptoms and medical history and conduct a physical examination depending on the infection. If this is not sufficient for an assessment, further tests may follow. These include:
- PCR test: The polymerase chain reaction, or PCR, looks for the genetic material of a specific pathogen. This method may be familiar from the COVID-19 pandemic.
- Blood test: Certain blood values can indicate whether there is inflammation in the body. While these values can aid in assessment, they do not always provide a definitive answer on their own.5
- Examination and cultivation of bacteria: If a bacterial infection is suspected, swabs, urine, or blood samples can be examined. In the lab, bacteria can be stained and viewed under a microscope or cultured on a nutrient medium. This helps identify the bacteria and determine which antibiotics are effective against them.
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Why viruses are unaffected by antibiotics
Viruses operate fundamentally differently from bacteria. They cannot reproduce independently but instead invade human cells and use their processes. Therefore, many of the targets that antibiotics attack in bacteria do not exist in viruses.
Also interesting: 8 researched methods to boost your immune system
What are all viral infections?
Respiratory viral infections
Infections of the nose, throat, bronchi, or lungs are particularly common. These include colds, the flu (influenza), COVID-19, and RSV infections. Depending on the virus, symptoms such as runny nose, cough, sore throat, or fever may occur.
Gastrointestinal viral infections
The stomach and intestines can also be affected by viruses. Typical examples are infections with noroviruses or rotaviruses. Common symptoms include nausea, vomiting, and diarrhea.
Other viral infections
Viruses can also affect numerous other organs and tissues. Known viral diseases include herpes, Epstein-Barr virus-induced mononucleosis, measles, or rubella. Some viruses are transmitted by mosquitoes or ticks, such as the dengue, chikungunya, and Zika viruses.