No doubt you’ll recall that when Dorothy actually encountered a lion in OZ it was slapped in the face and broke down crying — sort of a paper lion.

Despite the overwhelming evidence discounting a causative association between vaccines, Tylenol, circumcision, and autism, RFK Jr. simply will not concede that his beliefs are unwarranted. His fear of what could lurk in the woods — lions and tigers and bears — is now driving America’s health system.

Tylenol, also known by its non-commercial names acetaminophen and paracetamol, is readily available in almost every country on the planet. First synthesized in the mid-19th century, its ability to treat fever and pain was discovered accidentally. It has been available without a prescription since 1955 in the U.S.

There have been multiple studies of Tylenol safety, including definitive studies that have demonstrated its safety and effectiveness in pregnant women when used as directed. That of course, is coupled with the decades-long routine use by billions of persons the world over with only rare adverse consequences.

None of that prevented President Donald Trump and Robert F. Kennedy Jr. from declaring that Tylenol may cause autism. They unequivocally advised, with no evidence, that pregnant women should not take Tylenol for pain and fever. Trump called repeatedly for pregnant women to “tough it out.” Multiple large-scale scientific studies have failed to identify an association of acetaminophen with autism or, for that matter, any neurodevelopmental disorders.

The trouble is that there is unimpeachable evidence that untreated fever and pain during pregnancy can cause harm to both mother and baby. A fetus exposed to temperatures greater than or equal to 100.4 degrees F can develop neural tube defects or suffer damage to the chorioamniotic membrane. The latter can lead to fetal death or premature birth and admission to a neonatal intensive care unit. Toughing it out is not a likely recommendation from responsible obstetricians, who rely on knowledge and experience.

One-half to three-quarters of women experience serious pain during pregnancy, frequently lower back pain. Failure to address that pain often leads to mental health conditions, including depression, that can persist beyond pregnancy. Pain can be effectively addressed with acetaminophen in conjunction with targeted exercises.

When I first heard RFK Jr., the head of America’s Health and Human Services, assert that circumcision is a cause of autism, I laughed out loud. What’s next? Mosquito bites?

A search on the PubMed site locates just over 13,000 publications on circumcision. More than half of them report reduced risk of various infections, including HIV. Others are about additional medical conditions associated with circumcision. Only one publication suggested a possible association of circumcision with autism.

The study relied entirely on national data registries, most of which had no specific information on autism disorder. In such registries, the recorded data varies in content and is subject to speculation. The possible association was limited to ritual circumcision routinely performed in Muslim and Jewish communities. This single study is not persuasive evidence of a link between circumcision and autism. The authors themselves extensively discussed the limitations of the study.

Now, RFK Jr. is going after the aluminum adjuvant in many approved vaccines.

An adjuvant is a substance that can bolster the immune response to vaccines. Several aluminum compounds have been recognized for their usefulness as adjuvants since the 1920s. Vaccines containing aluminum include hepatitis A, hepatitis B, vaccines for diphtheria and tetanus, Haemophiles influenzae B, human papilloma virus, six meningococcal vaccines, and pneumococcal vaccines. Live attenuated vaccines (measles, mumps, rubella, varicella, and rotavirus) do not contain aluminum. Adjuvants are extensively tested for safety during vaccine evaluation trials and aluminum adjuvants are not harmful. Aluminum is present in very minute quantities, typically less than 1 milligram. Fully immunized infants will ingest as many as 27 times that much aluminum from baby formula alone during the first six months of life.

Removing the aluminum from vaccines will substantially reduce their effectiveness. Reformulation of vaccines will require new three-phase evaluation trials that will be prohibitively expensive.

RFK Jr.’s fixation on autism suffers from a number of failures in knowledge and logic. Between 80% and 90% of autism cases are hereditary.

That still leaves a subset of cases that are likely to develop through external exposures. Since 1990, shortly before the increase in cases was detected, roughly 60,000 new chemicals have been introduced into the environment. One (or more) of them might be responsible for cases of autism without a currently assignable cause, but we need to stop directing our efforts toward possible causes that have been definitively disproven.

Doing so is the scientific equivalent of chasing our own tail. Or believing in the threat of paper lions, tigers and bears.

D. Scott Schmid is an associate professor adjoint of molecular, cellular and developmental biology at the University of Colorado, Boulder