It depends on your baby’s age. If your baby is over six months and has a mild temperature, it’s fine to let the fever run its course.  A fever is more of a worry if your baby is less than six months old. It’s fairly unusual for young babies to develop a high temperature, so this can be a warning sign that something is wrong.  See your doctor straight away if your baby is:

• under three months and has a temperature of 38 degrees C or more
• three to six months and has a temperature of 39 degrees C or more

It’s sensible to take your baby’s temperature with a thermometer. But if your baby is older than six months, her temperature doesn’t always give the whole picture of how poorly she is. Your instinct that your baby is unwell is just as important.

Your baby has a fever because she’s fighting an infection or illness. Having a raised body temperature helps her immune system to fight the infection.  Sometimes, it may not be obvious why your baby has a fever, but common causes include: 

• Respiratory tract infections (RTIs). RTIs are any infection of the nose, throat, airways or lungs. RTIs include bronchiolitis, croup and whooping cough. In croup and whooping cough, the fever usually develops before the cough.
• Flu.
• Ear infection.
• A virus that causes a rash, such as roseola and chickenpox.
• Tonsillitis, which is an inflammation of the tonsils. It’s usually caused by a viral infection, but sometimes a bacterial infection can cause it.
• Kidney or urinary tract infections (UTIs).

Babies often get fevers after receiving immunisations. Your doctor or practice nurse will give you advice on what to look out for after your baby has had an immunisation. You may have heard that teething can cause a fever. However, although teething may make your baby miserable, it doesn’t cause a fever, or a bad tummy.

References:

Evans SS, Repasky EA, Fisher DT. 2015. Fever and the thermal regulation of immunity: the immune system feels the heat. Nat Rev Immunol 15(6):335-349

Sakulchit T, Goldman RD. 2017. Acetaminophen use and asthma in children. Can Fam Physician 63(3): 211–213. www.ncbi.nlm.nih.gov [Accessed March 2018]

Original article: https://www.babycentre.co.uk/a84/fever