There has been a great deal of medical information released in all the pomp and glory of a press conference by non-medical, non-pharmacist, or non-scientific persons about acetaminophen. There was a lot of misinformation and a great deal of opinions given.
Acetaminophen has been in our lives for a very long time. It was first synthesized in 1878 and first used to treat pain and fever in 1893. It has been in widespread use since the 1950’s and was marketed as an alternative to aspirin. (Aspirin is not recommended for use in children.) It was originally derived from coal tar, a derivative of coal from which we get several medicines and food and clothing dyes, especially the deep purple and blues. By accident a researcher investigating a treatment for intestinal worms was given the wrong chemical (acetanilide) which had no effect on worms but did lower fever. Acetaminophen was derived from the ineffective worm killer as a safe drug to reduce fever.
For 75 years scientists have been trying to determine exactly how acetaminophen works and recent studies have not yet determined how. It is felt to act on an enzyme called COX that is in the part of the brain called the hypothalamus. It is believed that it blocks the production of prostaglandins which then lowers the body’s temperature set point.
Prostaglandins are produced in response to triggers such as germs to increase the body’s temperature. The higher temperatures helps the body fight infections. When the production of prostaglandins is lowered the body’s temperature drops.
The heat of fever helps the immune cells perform, stresses the invading pathogen and infected cells, and combines with other stressors to provide an immune defense. Fever works by causing more damage to pathogens and infected cells than it does to healthy cells. When talking about healthy children, it is the cause of the fever that hurts the child, not the fever.
This is not necessarily true for the unborn child. Hyperthermia is a body temperature over 101 degrees F. Hyperthermia happens when the body absorbs more heat than it releases. This could be fever from an infectious disease, long exposure to hot days, hot tubs or extreme exercise. There is a small chance that infants in the first three months exposed to maternal hyperthermia from any cause have an increased risk of neural tube defects, cleft lip and/or palate, heart defects or preterm births.
A few studies reported a small increase in Attention Deficit Hyperactive Disorder and autism when mother had a fever in pregnancy, especially if the fever was NOT treated.
It is not clear exactly how overheating impacts the unborn infant’s development but animal studies suggest that heat may cause cell death and interfere with certain proteins involved in fetal development during the first three months.
Pregnant women should avoid activities associated with overheating and if there is a fever over 101 degrees, they should call their doctor. Heat seems to be more dangerous than acetaminophen for the unborn baby.
Sally Robinson, MD
Professor, UTMB Dept. of Pediatrics
Keeping Kids Healthy 10/2025