Asked by Philip
What is fever
Answers
Answered by
GPT-5 mini
Fever is an elevation of body temperature above the normal daily range, usually caused by the body’s immune response to infection or inflammation. It is a symptom, not a disease itself.
Key points
- Normal body temperature averages about 36.5–37.5°C (97.7–99.5°F) but varies by person, time of day, and measurement site.
- Fever is commonly defined as a temperature ≥38.0°C (100.4°F).
- Typical categories (approximate):
- Low-grade: ~37.5–38.3°C (99.5–100.9°F)
- Moderate: ~38.4–39.4°C (101.1–102.9°F)
- High: ~39.5–40.9°C (103.1–105.6°F)
- Hyperpyrexia: ≥41.5°C (≥106.7°F) — medical emergency
Causes
- Most often infections (viral, bacterial, fungal, parasitic)
- Inflammatory diseases (autoimmune), medications (drug fever), heat-related illness, immune reactions, malignancy, and other systemic conditions
How fever develops (brief)
- Foreign substances (exogenous pyrogens) or immune signals stimulate release of endogenous pyrogens (IL‑1, IL‑6, TNF, etc.).
- These stimulate prostaglandin E2 production in the hypothalamus, which raises the body’s temperature set point. The body then generates heat (shivering, vasoconstriction) until the new set point is reached.
Symptoms
- Feeling hot or cold/chills, sweating, headache, muscle aches, loss of appetite, malaise, dehydration.
- In children, fever can sometimes trigger febrile seizures (usually benign but alarming).
Fever vs hyperthermia
- Fever: hypothalamic set point is raised; antipyretics (acetaminophen/ibuprofen) usually help.
- Hyperthermia (heatstroke, drug reactions): body temperature rises without a changed set point; antipyretics are less effective and rapid cooling is required.
When to seek medical care (general guidance)
- Infants under 3 months with rectal temperature ≥38.0°C (100.4°F): urgent medical evaluation.
- Infants 3–6 months with fever ≥38.0°C or any concerning symptoms: contact provider.
- Any age: severe symptoms (difficulty breathing, severe pain, persistent vomiting, decreased responsiveness, stiff neck, new rash, signs of dehydration, confusion), fever ≥41°C, or fever lasting more than 48–72 hours.
- People who are immunocompromised or have serious chronic illness should seek earlier evaluation.
Treatment and self-care
- Fever itself often helps fight infection; treatment is aimed at comfort and preventing complications.
- Supportive care: rest, fluids to prevent dehydration, light clothing, a comfortable room temperature.
- Antipyretics (e.g., acetaminophen/paracetamol or ibuprofen) reduce fever and improve comfort — follow dosing advice from a clinician or the medication label. Avoid aspirin in children (risk of Reye syndrome).
- Cooling measures: tepid sponging or cool compresses can help with comfort; avoid alcohol baths.
- For severe or very high fevers, or if you’re unsure, contact a healthcare professional.
If you want, tell me the person’s age, exact temperature, measurement method (oral, rectal, tympanic, axillary), and any other symptoms — I can give more specific advice.
Key points
- Normal body temperature averages about 36.5–37.5°C (97.7–99.5°F) but varies by person, time of day, and measurement site.
- Fever is commonly defined as a temperature ≥38.0°C (100.4°F).
- Typical categories (approximate):
- Low-grade: ~37.5–38.3°C (99.5–100.9°F)
- Moderate: ~38.4–39.4°C (101.1–102.9°F)
- High: ~39.5–40.9°C (103.1–105.6°F)
- Hyperpyrexia: ≥41.5°C (≥106.7°F) — medical emergency
Causes
- Most often infections (viral, bacterial, fungal, parasitic)
- Inflammatory diseases (autoimmune), medications (drug fever), heat-related illness, immune reactions, malignancy, and other systemic conditions
How fever develops (brief)
- Foreign substances (exogenous pyrogens) or immune signals stimulate release of endogenous pyrogens (IL‑1, IL‑6, TNF, etc.).
- These stimulate prostaglandin E2 production in the hypothalamus, which raises the body’s temperature set point. The body then generates heat (shivering, vasoconstriction) until the new set point is reached.
Symptoms
- Feeling hot or cold/chills, sweating, headache, muscle aches, loss of appetite, malaise, dehydration.
- In children, fever can sometimes trigger febrile seizures (usually benign but alarming).
Fever vs hyperthermia
- Fever: hypothalamic set point is raised; antipyretics (acetaminophen/ibuprofen) usually help.
- Hyperthermia (heatstroke, drug reactions): body temperature rises without a changed set point; antipyretics are less effective and rapid cooling is required.
When to seek medical care (general guidance)
- Infants under 3 months with rectal temperature ≥38.0°C (100.4°F): urgent medical evaluation.
- Infants 3–6 months with fever ≥38.0°C or any concerning symptoms: contact provider.
- Any age: severe symptoms (difficulty breathing, severe pain, persistent vomiting, decreased responsiveness, stiff neck, new rash, signs of dehydration, confusion), fever ≥41°C, or fever lasting more than 48–72 hours.
- People who are immunocompromised or have serious chronic illness should seek earlier evaluation.
Treatment and self-care
- Fever itself often helps fight infection; treatment is aimed at comfort and preventing complications.
- Supportive care: rest, fluids to prevent dehydration, light clothing, a comfortable room temperature.
- Antipyretics (e.g., acetaminophen/paracetamol or ibuprofen) reduce fever and improve comfort — follow dosing advice from a clinician or the medication label. Avoid aspirin in children (risk of Reye syndrome).
- Cooling measures: tepid sponging or cool compresses can help with comfort; avoid alcohol baths.
- For severe or very high fevers, or if you’re unsure, contact a healthcare professional.
If you want, tell me the person’s age, exact temperature, measurement method (oral, rectal, tympanic, axillary), and any other symptoms — I can give more specific advice.
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