Fever is a common symptom of many illnesses and can indicate that your body is fighting off an infection. In this article, we will discuss what a fever is, the symptoms of a fever, how to determine a fever without a thermometer, normal human temperature readings in different age groups, what is considered a high temperature for adults and children, information about having a low body temperature, how to treat a fever, causes of fever, and when to seek medical attention for a high fever.


What is a fever?

A fever is an increase in body temperature that is usually caused by an infection, illness, or injury. The average normal body temperature is around 37°C (98.6°F), but it can vary from person to person and can also fluctuate throughout the day. A fever is usually considered to be a body temperature of 38°C (100.4°F) or higher.

A fever helps your body fight infections by stimulating your immune system (your body’s natural defence). By increasing your body’s temperature, a fever makes it harder for the bacteria and viruses that cause infection to survive. 


Symptoms of a fever

Symptoms of a fever can vary from person to person, but common symptoms include:

  • High body temperature
  • Sweating
  • Chills
  • Shivering
  • Headache
  • Muscle aches
  • Fatigue
  • Dehydration
  • Loss of appetite


How to determine a fever without a thermometer

If you do not have a thermometer to measure your body temperature, there are other ways to determine if you have a fever. You can check for signs such as a flushed face, rapid breathing, and a rapid heartbeat. You can also touch your skin to see if it feels warm or hot to the touch.


Normal human temperature readings in different age groups

The normal body temperature can vary depending on age. Here are the average normal body temperatures for different age groups:

  • Adults: 36.1°C to 37.2°C (97°F to 99°F)
  • Children: 36.6°C to 38°C (97.9°F to 100.4°F)
  • Infants: 36.6°C to 38°C (97.9°F to 100.4°F)


What is considered a high temperature for adults and children?

A high temperature is usually considered to be a body temperature of 38°C (100.4°F) or higher for adults and children. However, this can vary depending on the individual's baseline temperature and other factors such as age and underlying medical conditions.


Information about having a low body temperature

A low body temperature, also known as hypothermia, is a body temperature below 35°C (95°F). This can be caused by exposure to cold temperatures, certain medical conditions, or medications. Symptoms of hypothermia can include shivering, confusion, drowsiness, and a slow heart rate. If you suspect someone has hypothermia, seek medical attention immediately.


How to treat a fever

If you have a fever, it is important to stay hydrated and get plenty of rest. You can also take over-the-counter medications such as paracetamol or ibuprofen to reduce fever and relieve symptoms such as headache and muscle aches. However, if you have underlying medical conditions or are taking other medications, consult with a healthcare professional before taking any medication.

Here are some other things you can do to help the uncomfortable feelings associated with a fever:

  • Wear loose comfortable clothing
  • Make sure the room you’re in isn’t too warm
  • Avoid alcohol, as this can make dehydration worse

Make sure that you:

  • Don’t overdress
  • Don’t attempt to make yourself feel cold


Causes of fever

Fever can be caused by a variety of factors, including:

  • Infections such as the flu, colds, or pneumonia
  • Tonsilitis
  • Kidney or urinary tract infections (UTIs)
  • Inflammation due to autoimmune diseases or other medical conditions
  • Certain medications
  • Heat exhaustion or heat stroke
  • Cancer


When to seek medical attention for a high fever

Contact your GP practice if:

  • You have severe thirst or are urinating less
  • You are passing urine that is darker than normal
  • You are light-headed or weak
  • You have new, severe muscle cramps
  • Your symptoms have worsened or you notice new symptoms
  • You’ve had a fever after recent foreign travel

If your GP practice is closed, phone 111.


Contact your GP practice immediately if you have a fever and:

  • You are on treatment for immune deficiency
  • You are on immune-suppresant drugs, such as regular steroids, methotrexate, azathioprine or cyclophosphamide
  • You are taking medication where you have been warned about the risk of a reduced immune system
  • You are on, or recently completed, treatment for cancer, leukaemia, or lymphoma
  • You are a transplant recipient
  • You are HIV positive
  • You have chronic lung disease
  • You have asthma which has been treated with medication in the last 3 years
  • You have heart disease (excluding blood pressure which is currently well controlled)
  • You have diabetes or another metabolic disease
  • You have chronic gastrointestinal or liver disease
  • You have chronic renal (kidney) disease
  • You have cystic fibrosis
  • You have neurological conditions such as cerebral palsy, stroke, multiple sclerosis, or muscular dystrophy
  • You have sickle cell disease

If someone is not conscious and alert, or is not responding normally, phone 999 and ask for an ambulance.

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