Digital Thermometers: Choosing and Using Them for Older People

Types of home thermometers

Digital stick thermometers (oral, armpit, rectal). A small probe with a digital display. They are inexpensive, accurate when used correctly and can be used under the tongue, in the armpit or, with a suitable model, in the rectum. They take from about ten seconds to a minute and beep when ready. These are the most practical for most homes.

Ear (tympanic) thermometers. They measure infrared heat from the eardrum in about a second. They are quick and handy for a person who cannot hold a probe under the tongue, but results depend on a correct angle, and earwax, a small or bent ear canal or a recent ear infection can distort them. Ask a nurse to show the correct technique.

Forehead (temporal artery) and non-contact infrared thermometers. They scan the skin of the forehead without touching or with light contact. They are fast and hygienic but can be affected by sweat, a cold or hot room, distance and technique. Many clinicians treat them as screening devices and recheck with another method if the number is odd or the person seems unwell.

Mercury thermometers. Once common in Indian homes, they are being phased out. The glass can break and release mercury, which is toxic. They take longer and are hard to read. Avoid them, and if you have one, do not throw it in household waste; ask the local health authority or hospital how to dispose of it safely. Never put a glass thermometer in an older adult's mouth if they may bite, cough or be confused.

Strip and pacifier-type thermometers are not suitable for adults.

Which is best for an older adult?

Many families choose a digital stick thermometer for oral or armpit use, with a flexible tip and a large display, plus an ear or forehead model as a backup for a person who is asleep or restless. Look for:

• A large, clear display, ideally backlit, readable by older eyes.
• A beep when the reading is done, and a fever alarm.
• A memory of the last reading, for logging.
• A waterproof or easy-to-wipe body.
• A battery that is easy to change; keep a spare.
• A reputable maker, with a stated accuracy of about plus or minus 0.1 to 0.2 degrees Celsius for stick types.
• A talking model for a person with poor eyesight; see home monitoring with poor eyesight or tremor.

Costs vary, so pick quality over novelty features. See health device budgets and quality checks in India.

How to take a temperature

Preparation for any method. Wait at least 15 to 30 minutes after hot or cold drinks, smoking or exercise, a hot bath and heavy blankets, because they change the reading. Wash hands and clean the thermometer.

Under the tongue (oral). Only if the person is alert, can hold the probe safely and breathes through the nose.

1. Switch on and check the display is clear. 2. Place the tip under the tongue, to one side of the middle, deep in the pocket. 3. Close the lips gently around it. Do not bite. 4. Breathe through the nose until it beeps. 5. Read, record and clean.

In the armpit (axillary). Safer for confused or drowsy people, though less exact.

1. Dry the armpit. 2. Place the tip in the centre, against the skin, not through clothing. 3. Lower the arm and hold it close to the body, across the chest. 4. Wait for the beep. 5. Read and record. Axillary readings are usually a little lower, by around 0.5 degrees Celsius, than oral readings. Note the method in the log.

Ear. Pull the ear gently up and back to straighten the canal, insert the probe snugly and press the button. Use a clean probe cover. Take two readings from the same ear if unsure.

Forehead. Follow the maker's instructions on distance and spot. Make sure the forehead is dry, uncovered and not freshly wiped or chilled. Wait a few minutes after coming in from outside.

Rectal. Used mainly for infants and, under advice, in hospitals; not usually needed at home for older adults.

What the numbers mean in general

• Typical oral body temperature is often quoted as about 36.1 to 37.2 degrees Celsius (97 to 99 degrees Fahrenheit), but this varies by person, time of day and method.
• Older adults often have a lower baseline, sometimes about 36 degrees Celsius or a little below, so a reading that looks normal may already be higher than their usual.
• A fever is commonly defined as 38.0 degrees Celsius (100.4 degrees Fahrenheit) or above. Some geriatric guidance counts a smaller rise above the person's own baseline as significant, which is why it helps to know their usual reading. See fever in older adults: why it can be subtle and when to call.
• A low temperature, below about 35 degrees Celsius (95 degrees Fahrenheit), in an older person who is cold, drowsy or confused needs medical attention; it may reflect hypothermia, infection or thyroid or other problems.

Always combine the number with how your parent looks and feels, and record the method used. See vital signs: normal ranges for older adults.

When to take a temperature

• When your parent feels unwell, shivery, hot or unusually tired.
• When they have new confusion, falls, poor appetite or reduced drinking, since infection often shows this way in older adults.
• When a doctor asks for monitoring during an illness; see monitoring an older adult during an acute illness at home.
• Once or twice to learn their baseline when they are well, ideally at the same time and by the same method.

Routine daily temperature checks in a well person are not needed.

Cleaning and care

• Clean after each use with soap and water, or an alcohol wipe on the probe, and let it dry. Do not submerge unless it is marked waterproof.
• Use probe covers with ear thermometers.
• Do not share oral thermometers without cleaning, and consider separate ones for each person, especially in a sick household.
• Store in the case, away from heat, damp and direct sun.
• Replace batteries when the display dims.
• Do not drop or bend the probe.
• Check against another thermometer in the same room occasionally; if two devices differ by more than about half a degree consistently, question the older one. See calibration, batteries and replacement of home health devices.

Common mistakes

• Taking an oral reading right after tea, water or smoking.
• Putting the tip in the cheek or holding the mouth open.
• Armpit readings through clothing or with a damp armpit.
• Using a forehead gun in a cold or windy place and trusting a normal result in a sick person.
• Ear readings with a dirty or wrongly angled probe.
• Taking readings repeatedly and chasing differences of a tenth of a degree.
• Assuming "no fever" means "no infection". Older people may not mount a fever.
• Giving fever medicines on a set schedule without medical advice. Ask the doctor or pharmacist what is safe for your parent.

Indian conditions

In summer, a very hot room or direct sun can raise skin temperature and distort forehead readings; check indoors in a cool spot. In winter and in air-conditioned rooms, cold skin can read low. Heat stroke can cause a high temperature without sweating and is an emergency. Humid weather can damage devices, so store them dry. If you use an old mercury thermometer, replace it with a digital one.

When to ask a professional

Show the thermometer to the doctor or nurse to confirm it is accurate and to learn the best site for your parent. Call the doctor the same day for a temperature of 38 degrees Celsius or above, or for a lower temperature with confusion, a fall, poor drinking, shivering, a new cough, burning urine or a wound that looks infected. Call 112 if your parent is very drowsy or confused, breathing fast, has a stiff neck, a fit, a very high temperature, very low temperature or cold clammy skin.