A rectal temperature uses a digital thermometer in your baby’s bottom. Use this method only when it is appropriate for your baby and you know how to do it gently. Ask your clinician to demonstrate it, follow the exact thermometer instructions and stop if you feel resistance. A rectal reading of 100.4°F (38°C) or higher is a fever. If your baby is three months old or younger, call the pediatrician immediately for that reading, even if your baby otherwise seems well.
I would keep two questions separate: “Can I take this reading safely?” and “Does my baby need medical care now?” You do not have to complete a temperature check before asking for help.
First: does your baby need help now?
Call emergency services if your baby has serious trouble breathing, turns blue or gray, is unresponsive or is suddenly very hard to wake. Do not delay emergency care to find a thermometer or repeat a reading. MedlinePlus describes these kinds of breathing and responsiveness changes as emergency signs.
Call the pediatrician immediately for a rectal temperature of 100.4°F (38°C) or higher in a baby three months old or younger. The AAP’s fever guidance applies even when there are no other obvious symptoms. Tell the clinician your baby’s exact age and how you measured the temperature.
If your baby seems seriously unwell but the number is below the fever threshold, seek help based on their condition. A reassuring-looking display cannot rule out illness.
Is a rectal check the right method for your baby?
U.S. pediatric guidance commonly identifies rectal measurement as the most accurate method for young infants. The Canadian Paediatric Society says to use a rectal thermometer only if you are comfortable doing so and a healthcare provider has shown you how to use it safely.
Guidance also differs by country. The NHS recommends a digital thermometer in the armpit for children under five. Follow your local care team’s advice rather than switching methods because another website uses a different approach. Report the method you actually used.
Rectal measurement is not suitable for every child. Seattle Children’s advises against it in children with cancer or weakened immune systems. St. Jude explains that injury to the delicate skin can increase infection risk in children receiving cancer care. If your baby has a medical condition, a problem around the anus, or specific instructions against rectal checks, ask the care team which method to use.
If you have not been shown how, cannot keep your baby and the device steady, or feel unsure, call for guidance. “I couldn’t get a rectal reading safely” is useful information to give a nurse. It is not a reason to postpone the call.
Get the supplies and instructions ready first
Choose a working digital thermometer whose instructions permit rectal use for your baby. A device designed for the ear or forehead cannot be used this way. Avoid glass thermometers. Check the model number, the battery compartment and the display before starting; do not leave a thermometer or loose batteries with your child.
Keep these items within your reach:
- The thermometer and its exact instructions.
- The lubricant allowed by that manufacturer.
- A new probe cover, if the device requires one.
- Cleaning supplies permitted by the manual.
- A diaper and a place to write the result.
Read the instructions for turning the thermometer on, distinguishing an old stored reading from a new one, and recognizing the completion signal. Also check whether it displays Fahrenheit or Celsius. Familiarity with a different thermometer does not tell you what this one’s symbols mean.
Lubricant instructions can differ
AAP and Nemours instructions mention petroleum jelly, but that is not suitable for every model. For example, the Vicks V901USV7 manual requires a disposable probe cover and water-soluble jelly, and specifically says not to use petroleum jelly. Use the instructions for the thermometer in your hand. If they conflict with what you were shown, ask the clinician or manufacturer before proceeding.
Choose a secure place where you can stay beside your baby throughout the check. Have everything ready so you will not need to reach away while supporting your baby or holding the thermometer. Another adult can help organize supplies, but the procedure should not become a struggle to force your baby still.
How to take the reading gently
These steps summarize AAP temperature-taking guidance and Nemours KidsHealth’s rectal-temperature instructions. Your clinician’s demonstration and your device’s instructions should guide the details.
- Clean and prepare the device. Wash your hands. Clean the thermometer as directed, fit a new cover if required and apply the manufacturer-approved lubricant to the tip.
- Position and support your baby. Common positions are belly-down across your lap or on the back with the legs gently bent toward the chest. Use the position your clinician has shown you, supporting your baby securely.
- Turn the thermometer on and wait until it is ready. Make sure you are starting a new measurement, rather than looking at the memory display.
- Insert only as directed, without force. The AAP specifies about ½ inch for babies younger than six months. For older babies its general guidance allows up to 1 inch, but a particular device may have a shorter limit or an insertion guard. Never exceed the device’s limit. Stop immediately if there is resistance.
- Keep hold of both your baby and the thermometer. Do not let go or leave it unsupported. Wait for the device’s completed-reading signal.
- Remove gently and read the screen. Record the number, unit, method and time. Then clean the device according to its instructions and wash your hands.
If any step is unclear, stop and ask for help before trying again. A drawing or a general measurement on a webpage cannot account for every thermometer’s shape.
HEALTH QUESTIONS COME FIRST
A temperature check can change tonight’s priorities.
The SleepBaby.org homepage describes the SleepBaby.org Method and its information about bedtime routines and baby sleep schedules.
If your baby may be ill, take care of the medical question first. A routine cannot interpret the thermometer, treat a fever or tell you that your baby no longer needs attention. Follow the care plan your clinician gives you, even when it changes the evening you expected.
At another time, when ordinary bedtime planning is the question again, you may want to think about how feeds, pajamas and settling fit together. Visit the homepage to read about the Method and decide whether its discussion of routines and schedules addresses what you want to explore.
This is a separate invitation to learn about everyday sleep planning, without a promise of fewer illnesses, faster recovery or uninterrupted sleep. Your baby’s immediate health needs set the priorities tonight.
Stop if the check is not going gently
Resistance means stop. Do not push farther, twist the thermometer to get around resistance or keep trying to reach a printed depth. The depth is a limit, not a target to force your way toward.
If your baby’s movement makes it impossible to keep the thermometer steady, stop rather than trying to finish the beep. If there is bleeding or you think an injury occurred, stop further rectal checks and contact a clinician promptly. Explain what happened, including the device used and any symptoms.
You can tell the care team that you need another way to check the temperature. The reason for measuring is to help care for your baby; completing one particular method is not the goal.
What does the number mean?
100.4°F and 38°C are the same fever threshold for a rectal reading. Do not subtract a degree to make it match an armpit or oral reading. MedlinePlus explains that the exact relationship between measurement sites is unclear. Give the clinician the actual result and method.
A rectal temperature below that threshold does not, by itself, establish that your baby is well. Pay attention to feeding, alertness, breathing and other changes. An unexpectedly low temperature can also need medical advice, particularly in a young or unwell baby. Tell the clinician the actual number rather than deciding that “not a fever” means “nothing is wrong.”
For an older baby, the action depends on age, symptoms, medical history and how long the illness has lasted. Ask your pediatrician for an age-specific call plan. Do not borrow a different child’s fever threshold, and do not use the color of a thermometer display as the whole decision.
If two thermometers disagree
Write down both results with their times and methods. For example, “99.6°F under the arm at 8:10 p.m.; 100.4°F rectally at 8:20 p.m.” Those are two observations, not numbers to average together. If the rectal reading meets the urgent call threshold for a young baby, make the call rather than collecting more readings first.
The note to have ready when you call
Baby’s exact age: ____
Temperature and unit: ____
Method: rectal / other ____
Time: ____
Feeding, wet diapers, breathing and alertness: ____
Other symptoms or recent changes: ____
Medicines already given, amount and time: ____
Say whether the measurement was interrupted, the display showed an error, or there was resistance. If you could not obtain a reading, say so directly. Ask what to do next, when to check again and which changes should trigger emergency care.
Keep the clinician’s instructions beside the note so another caregiver can follow the same plan.
Common problems during a temperature check
The screen shows “Lo,” “L” or an error
The meaning depends on the model and when the symbol appears. It may be a startup or measuring-range message rather than your baby’s completed temperature. Read the manual’s display guide. Do not write a symbol down as a normal reading, and do not keep inserting the thermometer to troubleshoot an electronic problem.
If the device is not working and your baby may be ill, call the care team. You can explain the symptoms and the device problem without first buying a replacement.
Your baby just had a bath or was heavily bundled
Nemours notes that a recent bath or heavy layers can affect the reading. If your baby is otherwise well, follow your clinician’s advice about allowing things to settle before measuring. Do not delay urgent care, dismiss a young infant’s fever or assume that every high reading is caused by warm clothes.
You removed the thermometer before the signal
Record that the measurement was incomplete. Check the instructions before deciding whether to repeat it. Repeated attempts are not useful if your baby cannot stay comfortably supported or you are unsure about the technique. Ask the clinician for the next step.
Someone suggests taking it every few minutes
Ask the pediatrician how often they want measurements and which method to use. Keep track of the baby’s condition between readings. A care plan is more useful than a growing list of temperatures with no clear action attached.
Optional: a thermometer with instructions you can follow
If you need a replacement, the Vicks Digital Stick Thermometer V901 is one named option to compare. The manufacturer lists rectal use. Check the exact model and its current manual before choosing it; the reviewed V901USV7 instructions require a disposable probe cover and water-soluble lubricant. I haven’t tested it, and this is not an accuracy ranking or a claim that an alarm can decide when your baby needs medical care.
Already-owned alternative: a working digital thermometer whose instructions permit rectal use may be suitable if your clinician recommends that method. Keep it labeled and reserved for rectal use. Check its preparation and cleaning instructions, and keep the device and batteries away from your baby. Calling for needed medical advice comes before shopping for equipment.
This section has no affiliate purchase link. As an Amazon Associate, SleepBaby.org earns from qualifying purchases through affiliate links elsewhere on the site.
Watch: the AAP on when a fever needs a call
In this American Academy of Pediatrics video, pediatrician Nathan Chomilo discusses fever and contacting your child’s doctor. It offers broader fever context; it is not a demonstration of rectal thermometer placement.
If the player doesn’t work: open the official AAP video or read the AAP’s written when-to-call guidance. The written guidance considers age and the child’s condition, including unusual drowsiness, worsening illness and other concerning symptoms. A young infant’s fever needs prompt medical assessment. Ask the clinician about any medicine rather than applying advice intended for an older child.
After the reading: care, clean up and share the plan
If medical assessment is needed, making that call takes priority. For a young infant with fever, ask the clinician before giving fever medicine. Do not give medicine simply to see whether a lower number makes the situation less urgent. The AAP’s when-to-call guidance emphasizes your child’s age and condition alongside the temperature.
Once the immediate care decision is made, clean and dry the thermometer as its manufacturer directs. Label it for rectal use and keep it separate from any thermometer used in the mouth. Store it and any batteries out of your baby’s reach. Do not assume a device can be boiled, soaked or put in a dishwasher.
If another adult takes over, share the actual reading and the clinician’s advice rather than saying only “the fever is better.” Include when a medicine was given, if one was directed, and the planned follow-up. This avoids a fresh round of guessing when you are both tired.
Questions parents often have
Is a rectal thermometer different from a regular digital thermometer?
Some are designed only for rectal use; others permit several measurement sites. Check the exact model. Once you use a thermometer rectally, label and reserve it for that use rather than switching it to the mouth.
Can I just feel the forehead?
Touch can alert you that your baby seems warm, but it cannot supply a reliable temperature reading. Use the measurement method your care team recommends, and call based on concerning symptoms even if you cannot obtain a number.
Does 100.4°F count, or does it have to be higher?
It counts. The rectal fever threshold is 100.4°F (38°C) or higher. Do not round the reading down or subtract a degree.
What if I am too worried to do a rectal check?
Tell the pediatrician. Ask for a demonstration or an alternative method and clear instructions about when to call. Your baby can receive medical advice without you first mastering a procedure that you do not feel able to perform safely.
Sources
- Nemours KidsHealth: How to take a rectal temperature
- Nemours KidsHealth: Taking your child’s temperature
- Canadian Paediatric Society: Fever and temperature taking
- Together by St. Jude: How to take a temperature
- Vicks: Digital Stick Thermometer V901
- NHS: Taking your baby’s temperature
- AAP: How to take your child’s temperature
- AAP: Fever and your baby
- Seattle Children’s: Temperature methods
- MedlinePlus: Temperature measurement
- MedlinePlus: Fever
- AAP: When to call the pediatrician
- MedlinePlus: When to use the emergency room for a child
- Vicks V901USV7: Official owner’s manual
KEEP THE READING AND THE CARE PLAN TOGETHER
Know the next step before the next check.
Record the actual reading and follow the advice appropriate for your baby. When ordinary bedtime routines and schedules are your next question, the SleepBaby.org homepage introduces the Method.
