How to check a 14-year-old's temperature accurately with basic thermometers

I can’t diagnose, but I can help you check his temperature more accurately with the tools you have and suggest when to seek care.

How to get a reliable temperature reading with what you have

• Oral digital thermometer (best if he can cooperate):
  • Wait 15 minutes after he’s been breathing through his mouth, drinking hot/cold fluids, or exercising.
  • Have him close his lips around the thermometer tip and keep it under the tongue toward the back for the full time the device indicates (usually until it beeps).
  • Make sure the tip is centered under the tongue, not in front where air escapes.
• Axillary (underarm) digital or glass thermometer:
  • Axillary readings are often 0.5–1.0°F (0.3–0.6°C) lower than oral. To improve accuracy:
    • Place the clean thermometer tip in the center of the armpit against skin (not clothing).
    • Press his arm snugly against his side and keep him still for the full time.
    • If axillary gives 98.8°F, oral might be about 99.3–99.8°F (rough estimate).
• Rectal (most accurate for children) — optional and sometimes recommended for younger children:
  • For a 14-year-old, rectal is usually not necessary unless you cannot get any other reliable reading and you suspect a high fever. If you consider it, know how to do it safely (use a lubricated digital thermometer, insert only 1–2 cm for older children, hold still until it beeps). If you’re not comfortable, don’t attempt it.
• Glass (mercury or spirit) thermometers:
  • Shake down before use. Use orally or axillary depending on instructions. Allow the full recommended time (often several minutes) before reading the scale carefully at eye level.

Interpreting values and what to watch for

• Fever thresholds (general adult/older child guidance):
  • Oral: fever generally ≥100.4°F (38.0°C).
  • Axillary: add ~0.5–1.0°F to estimate oral equivalent.
• Mild warmth and congestion with a cough often suggest a viral cold; many low-grade fevers are OK to monitor at home.
• Seek medical care or call your pediatrician/urgent care if any of the following occur:
  • Temperature ≥102°F (38.9°C) for a child this age that you can confirm.
  • Rapid breathing, difficulty breathing, wheezing, persistent chest pain.
  • Very lethargic, hard to wake, or confused.
  • Persistent vomiting, severe headache, neck stiffness, severe sore throat, or a rash that doesn’t blanch.
  • Symptoms worsen or do not improve after a few days, or you’re worried.

Symptom relief at home

• Keep him hydrated (water, clear fluids).
• Rest and light foods as tolerated.
• For fever or discomfort, acetaminophen or ibuprofen can be used per dosing guidelines for age/weight. If you use these, follow the package dosing chart or ask a pharmacist/pediatrician for the correct dose for a 14-year-old by weight. Do not give aspirin to children or teens.
• Use saline nasal drops/spray and gentle suction or steam (hot shower) for congestion.
• Encourage nose-breathing when possible; hand hygiene and tissues for cough/sneeze.

When in doubt

• If you remain unsure about his temperature or condition, call your pediatrician or a nurse advice line and describe symptoms and your thermometer readings. They can advise whether in-person evaluation or testing (e.g., for influenza or COVID) is recommended.

If you want, tell me:

• the exact thermometer types you have (digital oral, digital axillary, mercury glass, etc.),
• the latest exact readings you measured and how (oral/axillary), and I’ll help you interpret them and estimate if he likely has a fever.