When to Go to the Emergency Room for a Fever in an Adult

Call 911 for a fever with confusion, a seizure, difficulty breathing, a stiff neck, or a rash that looks like small bleeding spots under the skin. Those do not require a high number. The symptoms decide, not the thermometer.

Almost everybody asks the wrong question about fever. The question is not “how high is it.”

The American College of Emergency Physicians begins with the useful framing: “Fever by itself is not an illness, but a symptom for a range of medical conditions.” A fever is your body responding to something. What matters is what it is responding to — and that shows up in the symptoms beside it, not in the reading.

The list that actually decides it

ACEP says a fever may indicate a serious or life-threatening illness if it comes with any of these — and none of them requires a particular temperature:

• Pain or tenderness in the abdomen
• Nausea or vomiting
• Severe headache
• A stiff neck that resists movement
• Light hurting the eyes
• Convulsions or seizures
• Difficulty breathing
• Strange behaviour, or altered speech
• Mental status changes, confusion, difficulty waking, extreme sleepiness
• A rash — “particularly if it looks like small bleeding spots under the skin”

Read that last one carefully. Small bleeding spots that do not fade under the skin are the single most important rash description on this page, and they are the reason a rash with a fever is never a wait-and-see.

A stiff neck that resists movement, light hurting the eyes, and severe headache are three items that belong together in most people’s minds for a reason. With a fever, that combination goes straight to an emergency room.

And now the number, which is the least useful part

ACEP does give one. Their wording, and it needs handling rather than repeating:

A fever in an adult is not usually dangerous unless it reaches 103°F (39.4°C) or higher.

That sentence is true and it is the most misusable sentence on this subject. It describes the fever itself — how dangerous the temperature is as a temperature. It says nothing about the illness causing it.

So: 103°F is a reason to be seen. Below 103°F is not a reason to stay home. Meningitis, sepsis, pneumonia and a great many other serious illnesses can present with a fever well under that figure — which is exactly why ACEP’s own symptom list carries no temperature at all.

Do not use the number to talk yourself out of the list.

Come in

• 103°F (39.4°C) or higher
• Any fever with any symptom from the list above
• A fever that has lasted more than a few days, or keeps returning
• A fever with a new rash
• A fever in somebody with a weakened immune system, on chemotherapy, on immunosuppressants, after a transplant, or without a spleen — for that group the threshold is much lower, and if you are in it you have probably been told so already
• A fever after recent surgery, a recent hospital stay, or with an indwelling line or catheter
• A fever with shaking chills and feeling profoundly unwell, even if the reading is modest
• A fever in an older adult, where serious infection can present with confusion or a fall rather than with a high temperature
• A fever after travel
• A fever in pregnancy

Our emergency rooms are open every hour of every day and are walk-in, with CT, X-ray and a full laboratory in the building — which is most of what answering “what is causing this fever” actually requires. Go to the nearest one, and if another emergency department is closer to you, that one is the right answer tonight.

If you are unsure, come in — this list is not exhaustive and you are not expected to work out what your fever is a symptom of.

Children are a different question with different numbers

ACEP notes that “Fever is one of the most common reasons that parents visit an emergency department with a child.”

Do not apply anything on this page to a baby. Infant thresholds are lower, age-banded, and cited to the American Academy of Pediatrics — fever in a baby has its own page and the numbers on it are not the numbers here.

Questions people actually ask

It is 104°F but I feel all right. Come in. That is above ACEP’s figure, and how you feel is not a substitute for it.

It is 100.4°F and I feel dreadful. Feeling dreadful with a modest fever is worth taking seriously, particularly with shaking chills. And if anything on the symptom list applies, the reading is beside the point.

Should I take something to bring the fever down before coming? Come as you are, and say what you have taken and when. This page gives no doses. A fever that has been treated can read normal at the desk, which is worth us knowing rather than not.

How long is too long? More than a few days, or a fever that settles and returns, is a reason to be assessed — and a clinic is a good setting for that if nothing on the symptom list applies. Our clinics are open Monday to Thursday and Friday mornings, with appointments by phone.

Does the type of thermometer matter? Somewhat, and not enough to change your decision. Report what you measured and how.

I have had chemotherapy recently and I have a temperature. Be seen now, and say that first at the desk. For people whose immune system is suppressed, a fever is treated as urgent at a much lower threshold, and the people in that group are usually told this explicitly by their own team.

No fever at all, but I feel like I have one. Still worth acting on if you are unwell — some serious infections produce a low temperature rather than a high one, particularly in older adults.

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The symptoms decide, not the thermometer. Call 911 for a fever with confusion, a seizure, breathlessness, a stiff neck, or a rash of small bleeding spots. Both of our emergency rooms are open 24 hours a day, every day of the year — walk in, no appointment and no referral. Find your nearest emergency room →

Related reading: which door do you need · fever in a baby

Sources

50. Fever — Know When To Go — American College of Emergency Physicians. https://www.emergencyphysicians.org/article/know-when-to-go/fever

This article is general information, not a diagnosis, and it cannot account for your history or your medications. It gives no doses, and nothing on it applies to a baby. If you are unsure, come in — this list is not exhaustive and you are not expected to diagnose yourself. If it might be an emergency, treat it as one and call 911.