Overview

A fever is an increase in body temperature, often signaling the presence of an infection. While it can be uncomfortable, fever is usually harmless and may help the body fight illness. In most cases, a fever doesn’t require medical treatment unless it causes distress or is associated with other serious symptoms.

The average body temperature is around 98.6°F (37°C), but normal values can range from 97°F (36.1°C) to 99°F (37.2°C) or higher. Body temperature may vary based on age, activity level, or time of day. Older adults typically have slightly lower temperatures than younger individuals.

When Is It Considered a Fever?

A person is generally considered to have a fever if they show the following readings:

  • Rectal, ear, or forehead (temporal artery): 100.4°F (38°C) or higher

  • Oral (mouth): 100.4°F (38°C) or higher

  • Armpit (axillary): 99°F (37.2°C) or higher

When to Seek Emergency Care

Seek immediate medical attention if:

  • A baby under 3 months has any fever

  • A child left in a hot car shows symptoms of heat-related illness, including:

    • High fever with little or no sweating

    • Severe headache

    • Seizures

    • Stiff neck

    • Confusion or unusual behavior

    • Persistent vomiting or diarrhea

    • Irritability or unresponsiveness

    • Any symptom that alarms you

Treatment

For Infants and Children

Most children with fevers don’t appear seriously ill. Whether to treat a fever depends on the child’s level of discomfort.

Home care tips:

  • Offer plenty of fluids

  • Dress the child in light clothing

  • Use a light blanket if they feel chilled (remove when chills stop)

  • If your child is over 6 months, consider acetaminophen or ibuprofen based on proper dosing instructions. Always consult a healthcare provider if your child has other medical conditions or is taking other medications.

For Adults

Adults with a fever over 103°F (39.4°C) usually appear and feel unwell.

Self-care suggestions:

  • Drink fluids frequently

  • Wear light, breathable clothing

  • Use a light blanket for chills

  • Take over-the-counter fever reducers such as acetaminophen or ibuprofen. Follow dosing instructions carefully, especially if you have underlying health conditions.

Important Warnings

  • Do not give aspirin to children or teenagers, as it increases the risk of Reye’s syndrome.

  • Do not give any fever medication to infants without first speaking to a healthcare provider.

When to Call Your Doctor

For Children:

  • Unusual behavior or extreme fussiness not improving with fever treatment

  • Signs of dehydration: no urine for 8–10 hours, no tears when crying, dry mouth, refusal to drink

  • Stiff neck or headache

  • Abdominal pain

  • Trouble breathing

  • Rash or joint swelling

  • Fever lasting more than 5 days

For Adults:

  • Trouble breathing

  • Chest pain

  • Severe headache or stiff neck

  • Mental confusion

  • Abdominal pain

  • Repeated vomiting

  • Signs of dehydration: dry mouth, reduced or dark urine, not drinking fluids

  • Rash

  • Difficulty swallowing or urinating

Temperature Conversion Table

Fahrenheit (°F) Celsius (°C)
105°F 40.6°C
104°F 40.0°C
103°F 39.4°C
102°F 38.9°C
101°F 38.3°C
100°F 37.8°C
99°F 37.2°C
98°F 36.7°C
97°F 36.1°C
96°F 35.6°C

How to Take a Temperature

Use a digital thermometer for the most accurate readings. Common types include:

  • Rectal: For infants and young children

  • Oral: Under the tongue

  • Temporal artery: Forehead (infrared scanner)

  • Axillary (armpit) and tympanic (ear): Convenient but generally less accurate

Avoid glass thermometers containing mercury due to health and environmental risks.

Tips for Using a Thermometer:

  • Always read the instructions for your specific device

  • Clean before and after each use with rubbing alcohol or warm soapy water

  • Do not use the same thermometer for both rectal and oral use—have separate, clearly labeled ones

  • Never leave a child unattended while taking their temperature

Steps for Specific Temperature Readings

Rectal (Infants)

  • Lubricate the thermometer tip with petroleum jelly

  • Lay the child on their stomach or side, knees bent

  • Gently insert the tip ½ to 1 inch (1.3–2.5 cm) into the rectum

  • Hold steady until the device beeps

  • Remove and read the temperature

Oral

  • Place the tip under the tongue

  • Close the mouth until the beep indicates completion

  • Read the result

Temporal Artery (Forehead)

  • Sweep the thermometer gently across the forehead

  • Read the temperature as shown

Armpit

  • Place the thermometer against bare skin, not clothing

  • Hold firmly until the beep sounds

  • Read the result

Ear

  • Insert the thermometer gently into the ear as instructed

  • Hold steady until the reading is complete

  • Remove and check the result