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Why does a Fever Cause Delirium?

J. Beam
J. Beam

Delirium is an acute condition that causes a person to become unfocused and confused. Though there can be several causes of delirium, fever is one such cause. A fever can cause the confusion because elevated body temperatures interfere with the metabolic processes of the body. In order for a fever to cause this condition, the body would have to reach a temperature of at least 105 degrees Fahrenheit or more in most cases. Fevers of 104 degrees Fahrenheit or lower are considered moderate to low-grade fevers and typically do not cause delirium.

Like fever, delirium is a symptom of an underlying cause. The condition can also be caused by poison, brain injury, withdraw from certain addictive substances, severe shock, and diseases such as Alzheimer Disease or Huntington’s Disease. Delirium accompanied by high fever could mark infectious disease or any number of conditions of the body. Though these symptoms can help doctors make a diagnosis, they are typically not the only symptoms of a condition or disease.

Ibuprofen may help reduce a person's high fever.
Ibuprofen may help reduce a person's high fever.

Frequently with high fevers, confusion may be present as well as seizures. Again, seizures associated with high fevers are considered acute and may or may not be a sign of another problem. Typically, both confusion and seizures associated with excessively high fevers dissipate when the fever breaks. Because of the potential for complications of a high fever, determining when to seek medical attention for fever, especially in children, can be confusing to many people.

If fever exceeds 104 degrees Fahrenheit in children under the age of two, medical help should be sought immediately.
If fever exceeds 104 degrees Fahrenheit in children under the age of two, medical help should be sought immediately.

As a rule of thumb, if a fever goes higher than 105 degrees Fahrenheit or is accompanied by delirium or seizures, you should seek medical attention. Similarly, if a moderate-grade fever persists for more than three days or does not respond to fever-reducing medication such as acetaminophen or ibuprofen, you should see a doctor. If a high-grade fever is present, but responds to medication and is not accompanied by other symptoms, you should still follow up with a doctor. Consult a doctor for children under the age of two if fever exceeds 104 degrees Fahrenheit.

Discussion Comments


I am 23 years old. Looking back now it still terrifies me but I have a better understanding as to why it happened. A few months ago I collected my kids from school at 3pm but come half 3-ish, I started shaking and crying uncontrollably. I don't remember everything that happened but I do remember feeling gravely ill with a very high fever. Sweating, cold shivers, shaking uncontrollably, crying uncontrollably. I was sure I was having a panic attack. I remember rocking back and forth on the settee with all these symptoms including fogginess, confusion and what I now know was delirium.

I had recently burst a water blister on the sole of my foot and it was very painful, as in my state of mind I realized it was blood red, seeping and stinging. Looking at this blister I cried and shook and couldn't understand a thing but there was one thing on my mind: Necrotizing Fasciitis AKA flesh eating bug. I was so delirious that I was adamant I had this infection.

I picked up my phone to dial 999 for an ambulance. For whatever reason I can't remember, I ended up phoning my dad instead. He too was ill, as was the rest of the family. I told him my delirious thoughts through tears and he handed me paracetamol and told me to get some sleep. Safe to say, the paracetamol brought my temp right down and I started feeling better. Sounds so stupid now, but in that state of delirium it felt so real. I'll never forget that.


Two years ago I had a fever of 106 with delirium. It was caused by sepsis from a kidney stone I had. I was in the shower when the onset occurred. I cannot remember anything that happened during that hour and half. I came to myself in the ambulance. I have had a difficult time coping with that episode, especially when I take a shower and realize that was the very place I became delirious. I find myself asking questions about what I did during that time period even two years later.

I post this to implore anyone who has a loved one who has experienced delirium to have compassion on them, and try and answer their questions as often as they feel they need to ask. It is difficult to process the fact that there was a period of time in your life you did not even know you existed.


I have had a few scary delirious episodes from fevers. When I was younger, I recall one when I had flu that involved me being strung up in a dark cave between two corpses. Another was about a news report about a guy who had died. I don't recall how he died, it was years ago, but I do remember going to his parent's house, and seeing his grave in their back garden and feeling this immense sense of sadness, and wondering why the heck he was buried in their back garden lol (he wasn't of course). This also involved me having the impossible task of trying to tell the entire city that he was buried there, and if I succeeded, I could sleep lol. Impossible tasks seem to be a common thread for me if I get fevers now. It's more of a feeling than imagery, like trying to push the opposing poles of two magnets together, and not being able to until the fever is gone. If I am stuck in a 'fever dream' in my sleep and something wakes me up, I'll think I am still in the dream and I'll be very confused and disoriented for a while after.


Good post. When I had a fever I'd have delirium in my sleep. Once I thought because I hadn't done something (I don't know what) I had killed most of the earth's population and only like one million were left. Another time, my parents had told me that I had led them around the house looking for something, and all of this happened when I was still half asleep or so.


I don't know if this is the same thing, but my 12 year old son got a high fever and he started talking randomly. He doesn't cry or anything but he'll just lie in bed, look lost and you can tell he's not there and he'll start talking about random stuff. A recent one was that he's in a tank shooting all the bad guys, so I asked how many of the bad guys are there, and he replied 18 of them. We can talk for like, 10 minutes, while I'm giving him water and putting a wet cloth on his forehead and I can tell that he's fully there.


My stepson gets this every time he is sick with a high fever, usually strep throat. He will wake up in a panic breathing hard and usually crying very load, screaming and moaning. He cannot not get many words out, maybe one or two. He is extremely scared when this happens. He hallucinates and things in his room become very large.It is extremely important to calm them down. Be gentle and loving. Make sure they feel safe and loved. I sit with him on the couch and talk to him about peaceful things. You have to assure them they will be fine. I immediately get two washcloths and put one around his neck and have him wipe his face down and hold it on his forehead. After about 15 minutes he will calm down enough to where he can go back to bed.

It is extremely important to know they are very scared and you have to calm them down gently.


I have been researching hallucinations as a result of fever all night, trying to find a name for it but haven't had any luck. I went to a doctor as a child when I was having these problems and the doctor gave me a name for it. It started with a K or C I think but I can't remember it anymore. Anyway, it's not an uncommon problem. It happened to me lots as a child whenever I got any bug that all the other kids were passing around, and has even happened to me a handful of times in my adult years, although to a much lesser degree.

I would compare the experience to a psychedelic trip. Anyway, although it's scary for everyone involved, ultimately it will pass and they will not be harmed by it in the long term. It's just your job to be as comforting as possible in the meantime. My mother would wait for the worst part to pass then gently find a way to get me to lie down and put a hot wet facecloth on my forehead, and that would bring me out of it. Talking in calm and quiet voices and using gentle touches is very important to bringing them out of it without frightening them too much, but they will always be somewhat startled and confused when they start to return to normal. Hope this helps someone.


I used to have delirium and hallucinations when I became sick as a child. I hated them! Sounds were distorted, people would talk really fast and then really slow. Sounds were magnified and just the sound of my dog walking up the hall to see what was wrong with me would scare me so bad. I could hear the click of her paws on the floor and to me it sounded like a monster coming for me.

Also, I would have dreams that involved large construction equipment that would come after me. To this day I am fearful of large road equipment. To my touch things would be soft and then suddenly rough, or cold and then very hot. My moms face would be distorted when I'd look at her. Mom would put tepid wash clothes on my face and I remember that they felt ice cold. When my fever would finally break I would return to normal but tired from the emotional stress and illness.


my two year daughter recently has episodes of delirium that terrified both my husband and myself. she was afraid of my face and was afraid of her skin. she thought something was on her and screamed in terror for them to get off. this went on for an hour until her fever came down and the er doc said that her symptoms were caused by her fever. i hope she never experience this ever again.


When I was little, I remember my uncle having a very serious fever that caused him to have hallucinations and delirium.

I remember thinking that it was kind of funny at first, because I was a kid and had never seen an adult act like that, but it quickly became scary.

All I can say is, any fever that causes delirium is serious business, so if you or someone you know is having a fever with hallucinations or delirium, take them to the ER immediately.


@rallenwriter -- Sometimes delirium tremens can present with a fever, as well as hallucinations.

However, a very high fever can cause hallucinations on its own, especially in children.

Geriatric delirium and hallucinations can also be caused by several conditions, including severe infections, tuberculosis, and abdominal abscesses.

Other causes of fever and delirium in the elderly include cellulitis, urinary tract infection, and reactions to medication.


What can cause a fever with delirium and hallucinations?

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    • Ibuprofen may help reduce a person's high fever.
      By: Geo Martinez
      Ibuprofen may help reduce a person's high fever.
    • If fever exceeds 104 degrees Fahrenheit in children under the age of two, medical help should be sought immediately.
      By: Vadim Ponomarenko
      If fever exceeds 104 degrees Fahrenheit in children under the age of two, medical help should be sought immediately.
    • Fevers usually need to be above 104 degrees Fahrenheit to cause delirium.
      By: Ocskay Bence
      Fevers usually need to be above 104 degrees Fahrenheit to cause delirium.
    • A doctor should be consulted for persistent fevers.
      By: Shakzu
      A doctor should be consulted for persistent fevers.
    • Medical help should be sought if a fever goes higher than 105 degrees Fahrenheit or if symptoms persist for more than three days.
      By: Sanjay Deva
      Medical help should be sought if a fever goes higher than 105 degrees Fahrenheit or if symptoms persist for more than three days.