Fever Causes, Symptoms and Treatments

What temperature is defined as a fever?

The average body temperature is normally around 37°C (98.6°F), however it can change during the day due to factors including physical activity, food, sleep, and the time. Temperatures often reach their highest point in the evening and their lowest point in the morning.

Infants and young children often have slightly higher temperatures compared to adults. Because body temperature can differ from person to person, as well as by the time of day and how it is measured, there is not a fixed fever threshold. However, healthcare providers usually consider a fever to be 38°C (100.4°F) when taken orally.

What is a low-grade fever?

A low-grade fever refers to a minor rise in body temperature, which shows a gentle immune response. While there is not a specific range, many medical professionals define low-grade fevers as temperatures between 37.5°C (99.5°F) and 37.9°C (100.3°F).

Symptoms of Fever

A thermometer is the best tool for accurately measuring a fever, but you might also observe some signs such as a warm forehead, which is best felt with the back of your hand, flushed cheeks, or feeling hotter than those around you. Other symptoms can include:

• Chills, shivering, and feeling cold.
• Muscle aches and headaches.
• Fatigue.
• Sweating (either constant or intermittent).
• Warm skin.
• A rapid heartbeat.

Symptoms in babies and young children, may also include:

• Loss of appetite.
• Ear pain or tugging at ears.
• High-pitched crying.
• Increased irritability.
• Pale or flushed skin.
• Excessive thirst.
• Reduced urination.

Measuring Body Temperature

There are various ways to measure body temperature:

• Mouth (oral): The most common method for people aged four and above.
• Underarm (axillary): Less accurate, typically measuring 1°C lower than oral readings.
• Ear (tympanic): Needs correct positioning for accuracy; excessive earwax may affect results. Not recommended for children under three years.
• Rectal: The most accurate method for infants and young children but less commonly used in the UK.

The temperature readings from rectal and ear thermometers are typically about 0.6°C (1°F) higher than those from mouth thermometers. On the other hand, readings from forehead (skin) thermometers are typically around 0.6°C (1°F) lower than those from mouth thermometers. Mercury-containing glass thermometers are no longer advised; digital thermometers are the best choice.

Common Causes of Fever

Fevers can occur due to many different reasons, but the most frequent causes include:

• Bacterial infections.
• Viral infections such as flu or COVID-19.
• Gastrointestinal infections.
• Urinary tract infections.
• Skin infections.

Other potential causes include:

• Reactions to certain medications.
• Recent vaccinations.
• Autoimmune disorders.
• Heat exhaustion
• Rheumatoid arthritis
• Lyme disease
• Some forms of cancer

Diagnosing Fever

Your GP will use a thermometer to check for a fever. He can determine the cause of your fever and whether you require treatment after looking over your symptoms and sometimes performing certain tests. To treat the cause or alleviate the symptoms, your GP might recommend medication. If you require more intensive care, he may recommend that you see a specialist or a hospital.

Treating Fever at Home

For mild fevers (below 38.3°C / 101°F), medication is often unnecessary. Instead:

• Stay hydrated by drinking plenty of fluids.
• Rest as much as possible.
• Take a lukewarm bath (around 36.7°C / 98°F). Tepid water baths (30°C /85°F) or sponge baths can assist in reducing fever, too.
• Do not wear too many layers of clothing, as it can increase your body temperature.
• Use a fan, open a window, or apply a cool, damp cloth to the forehead.
• Stay away from alcohol and caffeinated beverages, as they can cause dehydration.

Over-the-counter drugs such as aspirin, paracetamol, ibuprofen, or naproxen may help relieve discomfort or fevers above 38.3°C (101°F). Never administer aspirin to children younger than 17 since it can cause Reye's syndrome, a dangerous illness.

When to Seek Medical Help

Adults should contact a healthcare provider if:

• The fever exceeds 39.4°C (103°F).
• It persists for more than three to four days.

Children should see a GP if:

• The fever lasts more than five days.
• It reaches 40°C (104°F).
• Medication does not reduce the fever.
• They show signs of unusual behaviour or difficulty breathing or urinating.

When to Go to A&E

Seek emergency care (call 999) if a fever is accompanied by:

• Severe abdominal pain.
• Nausea or vomiting.
• Intense headache.
• Stiff neck.
• Sensitivity to light.
• Seizures.
• Difficulty breathing.
• Confusion or slurred speech.
• Trouble waking up or feeling very sleepy.
• A rash with small bleeding spots under the skin.

When to Take a Baby to A&E

If an infant under three months has a fever, seek emergency care immediately, as their immune system is not fully developed. Older children should also be taken to A&E if they experience:

• Extreme drowsiness or sluggishness.
• Persistent crying.
• Difficulty swallowing or excessive drooling.
• Breathing difficulties.
• Severe abdominal pain.
• Dehydration (fewer wet nappies, less fluid intake).
• Coughing up blood
• A febrile seizure for the first time
• Unusually cold hands and feet or pale skin and lips

Risks of Untreated Fever

A fever that exceeds 41°C (105.8°F) can be harmful and may cause organ problems. Even mild fevers can pose risks for individuals with heart or lung issues because they can raise heart and breathing rates. Additionally, those with dementia might see a decline in their mental function.

Febrile Seizures

A small number of young children (about 2–4%) can have febrile seizures caused by a fever. Signs of these seizures may include shaking movements or loss of awareness. If a seizure goes on for more than five minutes or if the child's lips become blue, call 999. For shorter seizures, get medical help quickly.

Fever Dreams

Fever dreams are vivid, strange dreams that happen when your body temperature rises. The exact reason for these dreams is not fully understood, but they might be linked to heightened brain activity or changes in sleep patterns

Last Word

Although a fever might be uncomfortable, it usually means that your immune system is functioning well. While over-the-counter medications can help, mild fevers usually go away on their own. It is crucial to see a GP if a fever persists for an extended period of time or gets extremely high in order to rule out any major problems.

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