If your 5-month-old has a rectal temperature of 100.4°F (38°C) or higher, call your pediatrician. For babies between 3 and 6 months old, any fever at or above that threshold warrants a call, even if your baby doesn’t look particularly sick. While you wait to hear back or head to the office, there are several things you can do at home to keep your baby comfortable and safe.
How to Take an Accurate Temperature
A rectal thermometer gives the most reliable reading for a 5-month-old. Digital ear thermometers and temporal artery (forehead) thermometers also work, but rectal is considered the gold standard at this age. Armpit readings tend to run lower and can miss a true fever, so if you get a borderline number under the arm, follow up with a rectal check.
To take a rectal temperature, apply a small dab of petroleum jelly to the tip of a digital thermometer and insert it about half an inch. Hold it in place until it beeps. A reading of 100.4°F or above counts as a fever.
Keep Your Baby Hydrated
Fever increases fluid loss, and dehydration can develop quickly in a young infant. Offer breast milk or formula more frequently than usual, even if your baby only takes small amounts at a time. At 5 months, breast milk or formula is all your baby needs for hydration. Water and electrolyte drinks are not appropriate at this age.
Watch for signs that your baby isn’t getting enough fluid:
- Fewer than six wet diapers in a 24-hour period
- Dry mouth or cracked lips
- No tears when crying
- A sunken soft spot on the top of the head
Any of these signs alongside a fever means your baby needs medical attention right away.
Medication for a 5-Month-Old
Infant acetaminophen (the active ingredient in Tylenol) is generally the go-to fever reducer for babies this age. Dosing is based on your baby’s weight, not age, so check with your pediatrician or pharmacist if you’re unsure of the right amount.
Ibuprofen is a different story. In the United States, it’s widely restricted to infants 6 months and older because of safety concerns, and over-the-counter labels reflect that cutoff. Some research has found no higher rate of side effects in younger infants who were prescribed ibuprofen, but it’s still not recommended without a doctor’s guidance. Stick with acetaminophen unless your pediatrician specifically tells you otherwise.
Never give aspirin to an infant. It’s linked to a rare but serious condition called Reye’s syndrome.
Comfort Measures That Help
Dress your baby in one light layer of clothing. Bundling a feverish baby in blankets can trap heat and push the temperature higher. If your baby seems chilly or is shivering, a single light blanket is fine, but remove it once the shivering stops.
A lukewarm sponge bath can help bring a fever down, but it works best after you’ve already given a fever reducer. Without medication, the temperature often bounces right back up once the bath is over. Use water that feels comfortably warm to your inner wrist. Never use cold water, ice, or rubbing alcohol. These can trigger shivering, which actually raises the body’s core temperature and makes things worse.
Keep the room at a comfortable temperature. If the air feels warm to you, it’s probably too warm for a baby with a fever. A fan circulating air gently in the room is fine as long as it’s not blowing directly on your baby.
When to Call Your Pediatrician
For a baby between 3 and 6 months old, the Mayo Clinic recommends calling your doctor if your baby has any temperature of 100.4°F or higher. You should also call if the temperature is below that threshold but your baby seems unusually fussy, sluggish, or just “off” in a way that concerns you. Trust your instincts here. You know your baby’s normal behavior better than anyone.
A fever that lasts more than five days, even a low-grade one, can point to an underlying problem that needs investigation. Keep a log of your baby’s temperature readings, the times you took them, and any medication you gave. This information helps your pediatrician assess the situation quickly.
Signs That Need Emergency Care
Most fevers in 5-month-olds are caused by common viral infections and resolve on their own. But certain warning signs alongside a fever require immediate medical attention:
- Extreme sleepiness or unresponsiveness. If your baby is hard to wake up or doesn’t respond to your voice or touch, that’s a red flag.
- Difficulty breathing. Watch for fast, labored, or shallow breaths. If your baby’s chest pulls inward with each breath, or the lips or face turn blue, call 911.
- Seizures. Fevers can trigger febrile seizures, which look like uncontrollable shaking or stiffening of the body. These are frightening to witness but are usually brief. Lay your baby on a flat surface away from hard objects and call for emergency help.
- A rash that doesn’t fade when pressed, or purple spots on the skin. These can indicate a serious bacterial infection like meningitis.
- A bulging soft spot on the top of the head, which may signal increased pressure inside the skull.
- A stiff neck. If your baby resists moving their head or seems unable to bend their neck forward, this is another possible sign of meningitis.
- High-pitched, unusual crying that you can’t soothe with any of your usual strategies.
If you’re seeing any of these alongside a fever, don’t wait for a callback from your pediatrician’s office. Head to the emergency room or call 911.