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What It Means

What Does Fever Mean?

Fever is a temporary rise in body temperature. It often happens when the immune system responds to an infection or inflammation. Feeling warm or having chills does not always mean you have a fever; a thermometer is needed to confirm an elevated temperature. What is considered a fever can vary slightly by age and how the temperature is measured, but a temperature around 100.4°F (38°C) or higher is commonly used as a general guide in adults.

Emergency Warning Signs

Emergency Warning Signs

GET URGENT HELP

Some fever symptoms need immediate care

Seek emergency evaluation for a fever with trouble breathing, chest pain, a severe headache or stiff neck, confusion, fainting, a seizure, severe dehydration, a rapidly spreading rash, or marked worsening. Any fever in an infant younger than 3 months needs urgent medical assessment, as does fever in someone who is severely immunocompromised.

Possible Causes

Possible Causes of Fever

  • Viral infections such as colds, influenza, COVID-19, or stomach viruses.
  • Bacterial infections such as urinary tract infections, strep throat, pneumonia, or skin infections.
  • Other infections, including some parasitic or travel-related illnesses.
  • Inflammatory or autoimmune conditions that can trigger body-wide inflammation.
  • Heat-related illness, especially when fever-like symptoms follow significant heat exposure.
  • Medication reactions or a temporary response after vaccination.
  • Less commonly, cancers or other serious conditions.

Associated symptoms can help clinicians identify the cause, including a cough, sore throat, urinary symptoms, abdominal pain, or rash. Recent travel, medication changes, and how long the fever has lasted are also important clues. Recurrent or unexplained fever deserves medical assessment, particularly when other fever symptoms continue or worsen.

Duration Triage Table

What Fever Duration May Mean

PatternWhat it may suggestWhen to seek medical advice
Acute feverA short-lived infection or temporary inflammatory response is common.Seek advice sooner if the fever is high, worsening, or accompanied by concerning symptoms.
Subacute feverA fever lasting several days may reflect an infection that needs assessment or a less obvious cause.Contact a healthcare professional if it is not improving or has no clear explanation.
Chronic or recurrent feverRepeated or persistent episodes can be linked to ongoing infection, inflammation, medication effects, or another medical condition.Arrange a clinical evaluation, especially with weight loss, night sweats, weakness, or other persistent symptoms.

Relief Tips

How to Manage a Fever at Home

  • Drink water or an oral rehydration drink regularly, especially if sweating, vomiting, or having diarrhea.
  • Rest and avoid strenuous activity while you feel unwell.
  • Wear lightweight clothing and use light bedding rather than trying to induce heavy sweating.
  • Keep the room comfortably cool and avoid ice baths or rubbing alcohol on the skin.
  • Check your temperature with the same method when monitoring changes.
  • Use acetaminophen or ibuprofen only when appropriate for your age and health history and according to the label or a clinician’s instructions.
  • Do not give aspirin to children or teenagers unless a clinician specifically recommends it.

When to See a Doctor

When to See a Doctor for a Fever

  • Contact a clinician if the fever lasts longer than expected for the illness or keeps returning without a clear explanation.
  • Seek advice if symptoms are worsening or new symptoms such as persistent vomiting, severe pain, or a widespread rash develop.
  • Contact a healthcare professional if you cannot keep fluids down or have signs of dehydration.
  • Seek medical guidance sooner if you are pregnant, immunocompromised, or have a serious chronic condition.
  • Ask a clinician about fever in a young child, older adult, or anyone who seems unusually sleepy, weak, or difficult to wake.

Complications

Possible Complications of Fever

  • Dehydration can develop when fever-related sweating is combined with poor fluid intake, vomiting, or diarrhea.
  • Fever can cause weakness, poor sleep, reduced appetite, and difficulty carrying out normal activities.
  • A high temperature and fluid loss may worsen certain chronic medical conditions.
  • Some young children can have a brief febrile seizure during a rapid temperature rise, which requires medical guidance, especially if it is a first seizure or lasts longer than expected.

Diseases & Conditions

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