I tell parents the 5-Day Fever Rule on a daily basis, and everyone should know it. Here it is in a nut shell: If your child has a fever that lasts for 5 days, you should worry. Fever that lasts 5 days usually represents badness. Generally speaking, the fever that happens with viruses (with very few exceptions) lasts less than 5 days. So if your child has a fever that lasts longer than that, you are generally talking about more serious conditions. So…

Go to the doctor on the 5th day of fever (if other symptoms haven’t taken you there sooner).   

When you go to the doctor, be prepared for a “work up” (looking for the source of the fever), which may include blood work, urine, or respiratory/nasal swabs.

I just finished another call week today and most of the parent calls I got revolved around fever questions. As parents, we worry when our children look sick and are running a high temperature. While I have posted on fevers before (see Should I Worry About Fever), here are a few quick reminders.

What is a fever?

Fever is an internal body temperature of 100.4 Fahrenheit or 38 Celsius or greater. Normal body temperatures are in the 97-99 range (hence the 98.6 average).

What’s the best way to take a temperature?

  1. In infants younger than 1 year: Rectally (yep, up the actual rear end)—just use a cheap, digit thermometer. The silver tip goes in the rectum and then you squeeze the butt cheeks together until the thermometer beeps with the reading. While some studies support other methods as being reliable in infants, the rectal temp is still considered the “gold standard.”
  2. Toddlers, kids, and teens: various methods.
    1. Tympanic: Measured in the ear (this is the kind I own). It measures the infrared heat waves released by the ear drum. FYI, it doesn’t work great if you have a kid with super waxy ears.
    2. Temporal artery: Measured on the side of the forehead. It measures the infrared heat waves released by the temporal artery (which is just under the skin on the side of the forehead).
    3. Oral: Measured under the tongue (using a digital thermometer). Not very accurate (easily altered it you eat something hot or cold).
    4. Axillary: Measured under the arm (using a digital thermometer). Not a reliable measure (one I steer parents clear of).

When to worry?

  1. Remember the 5-Day Rule—if the fever goes beyond 5 days, seek medical care.
  2. Worry if there is a fever initially that goes away (for a few days) and then returns.
  3. Your child is lethargic, has a really bad associated symptom (say a wretched sore throat to go with that fever), or looks terrible.

How high is too high? Don’t be surprised….

I didn’t write a magic fever number to worry over. The great exception is newborns. Any fever over 100.4 in infants under 2 months must be seen by a medical doctor. Otherwise, a 103 fever doesn’t make me more stressed medically than a 101 fever. Fever is just the body’s way of mounting an immune response to something. Some people mount bigger responses than others. I know what you’re thinking (because I get calls every night about it), 104 degrees is toasty—I know. The number however, does not correlate to seriousness. Yes, kids are miserable that warm, but generally they can handle it (See article Febrile Seizures: Is Your Child at Risk? for the few exceptions to this rule). The reason to treat a fever is to make a kid more comfortable.

In short (I have digressed), keep the “worry on the 5th day of fever” rule in your mind. Stay cool!

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About The Author

Dr. Monica Wonnacott

I'm a pediatrician and a mom. I've been doing this doctor thing for 10 years, and love it. I'm known for giving parents the straight scoop without always sugar-coating it. And I believe in educating parents. The more you know, the better care you give your kids.

Dr. Monica Wonnacott, Pediatric Answers ™

I'm a pediatrician and a mom. Pediatric AnswersTM is where parents can get the straight scoop on their child's health, largely based on my experience in the office and at home. I don't diagnose on the site, so please don't ask. These are just my opinions. Use this site as a resource. And trust your parent gut.

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