This blog post is an updated response to an Ask an autism researcher question from 2013.
My daughter has just turned 8 and is severely affected by classic autism. She is non-verbal. Recently she had a fever and her behaviour changed dramatically. She wanted to be held, maintained eye contact for lengthy periods and most incredibly – spoke words very clearly! She said her brother’s name and repeatedly said “Mum”. I have to repeat how incredible this is as she is completely non-verbal. Please somebody research this phenomenon!
The behaviour change that you observed in your daughter is known to autism researchers. Researchers call this phenomenon the ‘fever effect,’ where some Autistic children display temporary changes in behaviour during a fever. We offer a brief overview below.
What Is the fever effect?
The fever effect refers to a temporary change in behaviour that some Autistic children display during febrile episodes (a temperature above 37.5 degrees Celsius after seven consecutive days of normal body temperature). It has been studied in recent years, offering some interesting insights.
What the research tells us
A 2007 study on this topic confirms your observations, albeit with a relatively small group of children. A larger study in 2017 found that parents of Autistic children reported that 17% showed behavioural changes with fever, including increased communication and fewer temper or behavioural incidents. This study developed a profile of children most likely to show this change. The findings suggest that children whose parents notice behavioural changes during a fever tend to have lower nonverbal, cognitive, and language skills than children whose parents report no changes.
More recently, a 2023 study used machine learning to analyse the Simons Simplex Collection (a clinical database), finding a similar prevalence of the fever effect in Autistic children (17%). Parents reported that behavioural change in Autistic children was associated (correlated) with an increased prevalence of autoimmune disorders, language disorders, and neuropsychiatric disorders. The researchers suggest a possible involvement of immune dysregulation in the fever effect.
Conflicting results
While these studies provide evidence for the existence of the fever effect, not all research agrees. For example, a 2022 study found that Autistic children and non-Autistic children had similar responses to fever, with both groups showing worsened social, emotional/behavioural, and somatic symptoms. Only 2% of parents reported that their children showed the fever effect in this study.
Conclusion
The research on the fever effect is interesting and relatively new. The few studies conducted suggest that the effect is not universal; while some Autistic children may show temporary behavioural changes during a fever, some experience no changes or experience heightened difficulties. More research is needed to fully understand the mechanisms and potential benefits for some Autistic people.
Thank you to Dr Elfriede Ihsen who authored the original version, published in 2013
Behavioural changes with Autistic Children and Fevers
I am the proud parent of a six year old verbal autistic boy and have found the opposite reaction. When ill ( especially with fever) he withdraws and stops talking for days. He won’t eat or drink and will not look at me or communicate at all. I have had to take him to hospital due to dehydration and spent hours trying to convince doctors that he is verbal and has high functioning autism.
Dear Shari,
thank you for your comments on our article. Your comment confirms a common finding that different children with ASD often have different reactions to events in their environment, in this case fever. ASD describes such a complex spectrum of disorders, and it’s not surprising that individual differences are also complex and significant.
Our article on reactions to fever was written in response to a question from a parent whose child reacted to a fever in a specific way and wanted to know if there is any research on this phenomenon. Our search of the literature confirmed that similar reactions had been recorded to have happened to other children with ASD. But as we say in our article, we don’t know how common these particular reactions are and why they occur. We may have added that we don’t know whether there are other reactions to fever experienced by children with an ASD and whether they are different to those experienced by typically developing children. We need more research on this issue.
Having said this we must emphasise that any child with a fever will need the standard medical treatment and must be monitored for complications.