Plus, a doctor explains the signs to look out for if you don’t have a thermometer.
How do you know when you have a high temperature or fever?
Your normal temperature fluctuates a little during the day, rising by a degree in the morning and is highest in the afternoon. However, when your core body temperature rises more than this, you have a fever. This can happen in infection and certain illnesses.
A fever is our body’s way of telling us something is off and shows your body is responding to a threat of some kind.
What is a normal body temperature?
For an adult, an average normal temperature measured with a mouth (oral) thermometer is 37°C and for a child 36.4°C to 37.4°C, an elderly person around 36.8°C.
If the number is higher than this, the adult or child has a fever.
However, the number will also depend on the method you use and whether you follow instructions correctly.
What type of thermometer should I use?
Thermometers can usually be purchased from a pharmacist who can advise you on the best type for you and your household. The main types are digital probe and ear. Glass thermometers are not ideal due to risk of breakage and of course poisonous mercury is no longer used. Replacing a glass thermometer with a digital one is far safer.
Digital or Probe Thermometer
These are the most common household thermometers and easy to measure temperature from the armpit or mouth. They are a handheld device with a little window that easily displays the temperature in numbers.
For children under five, it is suggested that you do an armpit measurement as long as they can sit still long enough. Very young children and babies sometimes have rectal temperature measured in hospital but this is after careful direction on use by a healthcare provider.
Ear (infrared) thermometer
These are commonly used by clinicians as easy to use on all ages but they are expensive and some argue less accurate if not used correctly. These thermometers have clean disposable probe covers.
With a child it is important that you gently pull the top of the ear gently backward as this clears the path to the ear drum where the measurement is taken. Following instructions, you then usually press a button and the digital result is displayed almost immediately.
Forehead or strip thermometer
These are the least reliable of all thermometer types as they only really measure the skin temperature not that at the core. They can give you a relative reading – whether things are going up and down – but the actual number is not so accurate.
How do I know if my thermometer is accurate?
There are a number of things that could affect the thermometer reading to make it inaccurate. These are:
- Not following instructions
- Measuring after being out in cold air or sitting in a hot bath
- Measuring after consuming a hot or cold drink or meal
- Being excessively wrapped in warm clothing or bedding
- Measuring after exercise
- Holding a hot water bottle, sitting by a fire, hot weather
- Having head on a warm pillow
Ideally, wait 10 to 15 minutes after your warm chicken soup or cuppa, or removing heavy bedcovers before taking your temperature. No need to strip down to be shivering, just not overheated, as shivering itself can raise a temperature further.
How do I clean a thermometer?
Make sure the thermometer is clean (wash with cool soapy water and rinse) and if they are available use a new disposable probe cover. It is fine to use the thermometer on different members of the household as long as you are rigorous about cleaning it in between.
Wash your hands before and after taking anyone’s temperature.
Can I check for a fever without a thermometer?
We often use the back of the hand to feel someone’s body warmth as it is an area allegedly more sensitive to temperature. However, this can be subjective. You might only be able to tell that one of you is warmer than the other, so this is not really reliable.
Burning up, sweating, shivering, feeling hot around the head, looking flushed, loss of appetite, aching can all be signs of a fever. You may actually feel cold rather than hot.
When to see a doctor for a fever
Most fevers on their own are not life threatening but if you have underlying health issues or worrying new symptoms, you will need to discuss with your healthcare professional.
Headache, rash, stiff neck, nausea, vomiting especially in children may be signs of severe illness which cannot be measured by temperature alone and are all reasons to discuss urgently with your healthcare professional.
In other febrile illnesses in all ages you may also have symptoms including chest pain, persistent cough, persistent diarrhoea, rashes, abnormal bleeding or bruising, reduced level of consciousness, problems passing urine or simply appear unwell to those around you. These would all be reasons to seek professional advice urgently.