Pyrexia
Pyrexia, commonly known as fever, is your body’s natural way of fighting infection. When your temperature rises above normal, it signals that your immune system is working hard to combat invaders like viruses or bacteria. While uncomfortable, this protective response plays a crucial role in helping you recover from illness.
Table of contents
- What Is Pyrexia?
- Symptoms and Signs
- Causes of Pyrexia
- Types of Pyrexia
- Diagnosis
- Treatment Options
- When to Seek Medical Help
- Potential Complications
- Prevention
What Is Pyrexia?
Pyrexia is the medical term for fever, which refers to an increase in body temperature above the normal range. Normal body temperature is typically around 98.6°F (37°C), though this can vary slightly from person to person and throughout the day[1][2]. A body temperature of 100.4°F (38°C) or higher is generally considered a fever[5].
Pyrexia happens when a part of your brain called the hypothalamus (the organ that regulates body temperature) increases your body’s temperature set point[2][3]. This increase in the set point triggers your body to produce more heat through increased muscle contractions, which causes you to feel cold or experience chills[2]. Your body is essentially creating an environment that is less favorable for harmful germs while boosting the effectiveness of your immune cells.
It is important to distinguish pyrexia from hyperthermia, which is a different condition. Hyperthermia occurs when your body absorbs more heat than it can release, and it does not affect the temperature set point in the hypothalamus[3]. Pyrexia is also different from hyperpyrexia, which is a medical emergency that occurs when body temperature rises above 106.7°F (41.5°C)[3].
Symptoms and Signs
When you have pyrexia, you may experience a variety of symptoms beyond just feeling warm. Initially, you might feel cold, shiver, or experience chills as your body works to raise its temperature[2]. As the fever progresses, you may feel flushed and start sweating[2].
Common symptoms that accompany pyrexia include[1][5]:
- Sweating
- Chills and shivering
- Headache
- Muscle aches
- Loss of appetite
- Irritability
- Dehydration
- General weakness
- Fatigue
If your fever becomes very high or persists, you may develop more severe symptoms such as confusion, extreme sleepiness, fast heart rate, or seizures[3][5]. These symptoms require immediate medical attention.
Causes of Pyrexia
The most common cause of pyrexia is infection[1][9]. When harmful microorganisms invade your body, your immune system responds by producing chemicals that reset your body’s thermostat to a higher level, creating an environment that is less hospitable to these invaders[4].
Infectious causes of pyrexia include[2][6][9]:
- Viral infections such as influenza, common cold, COVID-19, and other respiratory tract infections
- Bacterial infections such as tonsillitis, pneumonia, urinary tract infections, and appendicitis
- Parasitic infections such as malaria
- Fungal infections
Non-infectious causes can also trigger pyrexia[2][9][6]:
- Inflammatory disorders such as rheumatoid arthritis and ulcerative colitis
- Autoimmune diseases
- Side effects from medications or vaccinations
- Certain types of cancer
- Blood clots or deep vein thrombosis
- Heat stroke
- An overactive thyroid (thyroid storm)
- Brain trauma or tumor
Types of Pyrexia
Pyrexia can be classified into different types based on severity and pattern[4][6]:
Based on severity:
- Low-grade fever: Temperature between 99.1°F to 100.4°F (37.3°C to 38°C)[5]
- Moderate-grade fever: Temperature between 100.6°F to 102.2°F (38.1°C to 39°C)[5]
- High-grade fever: Temperature between 102.4°F to 105.8°F (39.1°C to 41°C)[5]
- Hyperpyrexia: Temperature above 106.7°F (41.5°C) — this is a medical emergency[3]
Based on pattern:
- Intermittent pyrexia: Temperature spikes periodically, followed by returns to normal[4]
- Remittent pyrexia: Temperature fluctuates but does not return to normal
- Continuous or sustained pyrexia: Temperature remains consistently elevated
- Relapsing pyrexia: Fever comes and goes in cycles[4]
Pyrexia can also be classified as infectious or non-infectious based on its underlying cause[6].
Diagnosis
To diagnose pyrexia and determine its cause, your healthcare provider will first take your temperature using a thermometer. Different types of thermometers can be used, including oral, rectal, ear, and forehead thermometers[1]. Rectal thermometers generally provide the most accurate measurement of core body temperature, especially in infants[1].
During your visit, your doctor will[1][8]:
- Ask questions about your symptoms, such as coughing, abdominal pain, vomiting, or pain when urinating
- Inquire about recent surgeries, injuries, or vaccinations
- Ask about new medications you may be taking
- Ask about recent travel, particularly to other countries
- Perform a physical examination
Based on your symptoms and medical history, your doctor may order additional tests[8]:
- Blood tests
- Urine tests
- Nasal or throat samples to test for respiratory infections
- Chest X-ray
- Other imaging tests as needed
When a fever lasts for more than three weeks without a clear cause, it is called a fever of unknown origin, and may require consultation with specialists for further evaluation[8].
Treatment Options
In most cases, a mild fever does not need to be treated as it is helping your body fight infection[7][9]. However, if the fever is causing discomfort or is high, there are several ways to manage it.
Home remedies and self-care:
- Rest: Get plenty of rest and stay home from work or school. Sleep helps your immune system work properly[12][17].
- Drink fluids: Drink plenty of water, herbal tea, juice, or broth to stay hydrated. Fever can cause sweating and fluid loss, increasing your risk of dehydration[9][12][17].
- Light clothing: Dress in light, breathable clothing and avoid heavy blankets[12].
- Lukewarm baths: Take a room-temperature or slightly cool bath or shower. Avoid very cold water, as this can cause shivering and raise body temperature[9][12].
- Cool compresses: Apply a damp washcloth to your forehead or wrists, or use a cold pack under your arm for up to 10 minutes at a time[17].
- Eat light foods: Try to eat light, easy-to-digest foods even if you don’t have much appetite[12].
Over-the-counter medications:
For fevers above 102°F (38.9°C) that cause discomfort, your healthcare provider may recommend[7][8][9]:
- Acetaminophen (Tylenol)
- Ibuprofen (Advil, Motrin)
Be careful to follow the dosing instructions on the label and avoid taking too much, as high doses can cause liver or kidney damage[8]. Adults may also use aspirin, but it should never be given to children under 18 due to the risk of a serious condition called Reye’s syndrome[8][17].
Medical treatment:
Treatment for the underlying cause of the fever depends on what is causing it. Bacterial infections may require antibiotics, while viral infections typically need supportive care and time to resolve[9]. It’s important to note that antibiotics are not effective against viral infections[9].
When to Seek Medical Help
While most fevers resolve on their own, certain situations require medical attention.
For infants and young children:
- Your baby is younger than 3 months and has a rectal temperature of 100.4°F (38°C) or higher
- Your baby is 3 to 6 months old with a temperature above 100.4°F and appears irritable or sleepy, or has a fever above 102°F for more than one day
- Your child is 6 months to 2 years old with a fever higher than 102°F for more than one day
- Your child has a fever with other symptoms like rash, severe discomfort, irritability, low energy, headache, stiff neck, or repeated vomiting or diarrhea
- Your child has a fever higher than 104°F, which can cause seizures
- The fever doesn’t go down after taking over-the-counter medications
For adults:
Contact your doctor or visit urgent care if[5][16]:
- Your temperature is 103°F (39.4°C) or higher
- Your fever doesn’t go down after taking over-the-counter medications
- Your fever lasts for more than three days
- You’ve been in contact with someone who has COVID-19
- You are pregnant with a fever of 102°F or higher
Seek immediate emergency care (call 911 or go to the emergency room) if you or your child experience[5]:
- Unresponsiveness
- Seizures or convulsions
- Wheezing or difficulty breathing
- Blue lips
- Confusion or speaking in a confused way
- Stiff neck with headache
- Temperature higher than 105°F
- Sudden onset of rash
- Severe stomach pain or persistent vomiting
- Skin rashes, blisters, or red streaks on arms or legs
- Severe sore throat or swelling of the throat
Potential Complications
Most fevers do not cause serious complications. However, certain situations can lead to problems that require immediate attention.
Fevers rarely go higher than 41 to 42°C (106 to 108°F)[2]. A fever of 42.4°C (108°F) or higher, particularly in elderly people, can permanently damage the brain[9][15].
In children between the ages of 6 months and 6 years, fever can trigger febrile seizures (convulsions caused by fever)[2][9][15]. While frightening for parents, these seizures are usually brief and don’t cause lasting harm.
Hyperpyrexia (temperature above 106.7°F or 41.5°C) is a medical emergency that can lead to serious complications if not treated quickly[3]:
- Pressure or swelling on the brain
- Permanent brain damage
- Coma
- Organ dysfunction affecting the heart, lungs, liver, kidneys, and gastrointestinal system
Dehydration is another potential complication of fever, especially if you are sweating heavily or experiencing vomiting or diarrhea[17]. This is why drinking plenty of fluids is so important when you have a fever.
Prevention
While you cannot prevent all fevers, you can reduce your risk of infections that cause fever by following these practices[9]:
- Wash your hands frequently with soap and water, especially before eating and after using the bathroom
- Teach children proper hand-washing techniques
- Avoid touching your nose, mouth, or eyes, as this is how germs easily spread
- Cover your mouth and nose when coughing or sneezing
- Avoid sharing cups, water bottles, and eating utensils with others
- Stay up to date with recommended vaccinations
- Maintain good overall health through proper nutrition, regular exercise, and adequate sleep
- Practice good hygiene
If you have a fever, stay home to avoid spreading illness to others and allow your body time to recover[12].
