What is the cause of pyrexia (fever)?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Article Review Status
Submitted
Under Review
Approved

Last updated: March 9, 2025 • View editorial policy

From the Guidelines

Fever is primarily caused by the body's immune response to an infectious pathogen, and it plays a crucial role in fighting and overcoming infections. The most recent and highest quality study, 1, published in 2016, highlights that fever is a normal physiologic response that may result from the introduction of an infectious pathogen into the body. According to this study, the majority of febrile children will have a benign, self-limited viral infection, but a small number of pediatric patients, especially those younger than 3 months, will have a serious infection.

Key Points to Consider

  • Fever is defined as a rectal temperature greater than 38°C (>100.4°F) 2
  • The risk of serious bacterial infections (SBI) varies by age, with neonates (aged 3 to 28 days) having a higher risk of 13% 1
  • The management of febrile pediatric patients involves differentiating between those with serious infections and those with benign, viral infections
  • Antipyretic use, immunization status, and the ability of parents or caregivers to monitor the infant or child are important considerations in management

Management Recommendations

  • For adults, take acetaminophen (Tylenol) 325-650mg every 4-6 hours or ibuprofen (Advil, Motrin) 200-400mg every 4-6 hours as needed, not exceeding maximum daily doses (4000mg for acetaminophen, 3200mg for ibuprofen)
  • For children, use weight-based dosing and children's formulations
  • Stay hydrated by drinking plenty of fluids, rest, and dress in light clothing
  • Apply cool compresses if comfortable
  • Seek medical attention if fever exceeds 103°F (39.4°C) in adults or 102.2°F (39°C) in children, persists beyond 3 days, or is accompanied by severe headache, stiff neck, confusion, difficulty breathing, rash, or persistent vomiting.

From the Research

Causes of Pyrexia (Fever)

  • Pyrexia, or fever, is a physiologic mechanism that has beneficial effects in fighting infection 3
  • Fever is not the primary illness, but rather a symptom of an underlying condition 3
  • The cause of fever can be due to various conditions, including viral or bacterial infections 4, 5, 6

Types of Infections that Cause Fever

  • Bacterial infections, such as bacterial fever, can cause fever 4, 5
  • Viral infections, such as the common cold, sore throat, and sinusitis, can also cause fever 4, 5, 6
  • Neoplastic or inflammatory fever can also cause fever 5

Treatment of Fever

  • Antipyretics, such as acetaminophen and ibuprofen, can be used to treat fever 3, 4, 5, 7
  • The choice of antipyretic may depend on the underlying cause of the fever, with some studies suggesting that paracetamol/ibuprofen combination may be more effective in patients with bacterial fever 5
  • The primary goal of treating fever should be to improve the patient's overall comfort, rather than focusing solely on normalizing body temperature 3

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.