Hello Health Rounds readers! Today we feature a Spanish study that found structural changes to the brains of babies in the womb if the mothers were exposed to high levels of certain pollutants in air. We also report on a new finding of how the widely used painkiller acetaminophen actually works, and a small but alarming rise in appendix cancers among young adults.

In breaking news, see these stories from our Reuters journalists: Kennedy replaces fired US CDC panel members, includes anti-vaccine proponents; US CDC restores jobs for 450 laid-off employees; Kennedy’s ouster of US vaccine advisors puts pharma ties under scrutiny; vaccine group Gavi seeks to broaden donor base as aid budgets shrink; and new US dietary guidelines expected as soon as this month.

U.S. states will not be able to fully administer food stamp benefits for the nation's poor if a proposal in the Republican tax bill forcing them to shoulder billions of dollars in new costs is signed into law, according to state officials, local government associations and policy experts.

Brain development in the womb is affected by the mother’s level of exposure to air pollution, researchers have found, although it’s not clear whether the brain structure differences observed will cause any issues later.

Researchers in Barcelona analyzed data collected between 2018 and 2021 from 754 mother-fetus pairs. During the third trimester of pregnancy, participants underwent transvaginal neurosonography, a specialized ultrasound that allows the analysis of fetal brain shape and structures.

Higher prenatal exposure to nitrogen dioxide, particulate matter, and black carbon in pregnant women's homes, workplaces, and commuting routes was associated with an increase in the volumes of multiple brain regions that contain cerebrospinal fluid, the researchers reported in The Lancet Planetary Health.

Higher exposure to black carbon was also linked with a reduction in the depth of a groove in the brain called the lateral sulcus, which the researchers said might suggest less maturation of the brain.

All measurements of brain structures were within the range considered normal, however.

“At this stage, we can only report having observed differences in the brains of fetuses with higher exposure to pollution compared to those with lower exposure,” senior study author Jordi Sunyer of the Barcelona Institute for Global Health said in a statement.

“Additional research is needed to determine whether these effects are reversible after birth or if they persist, and whether they have any implications for neurodevelopmental outcomes in later stages.”

Scientists have been wrong about how acetaminophen eases pain, a discovery that could lead to new pain management approaches, researchers reported in PNAS.

For decades, scientists believed that acetaminophen, the main ingredient in Tylenol - known in some countries as paracetamol - relieved pain by working only in the brain and spinal cord. But researchers have discovered the drug also works outside the brain, in the nerves that first detect pain.

After the drug is ingested, the body processes it into a metabolite called AM404. The new study found in laboratory experiments that AM404 is produced in pain-sensing nerve endings, where it shuts off specific channels that help transmit pain signals to the brain.

By blocking these sodium channels, AM404 stops the pain message before it even starts, the researchers said.

“This is the first time we've shown that AM404 works directly on the nerves outside the brain,” study leader Alexander Binshtok of Hebrew University in Israel said in a statement. “It changes our entire understanding of how paracetamol fights pain.”

The discovery could lead to new types of painkillers that mimic the effects of AM404, the researchers suggested. Because AM404 targets only the nerves that carry pain, such drugs may avoid some of the side effects of traditional painkillers, they said.

U.S. appendix cancer rates, while still low, have been climbing dramatically in younger adults, according to a report published in Annals of Internal Medicine.

Appendix cancer rates were three times higher among people born between 1975 and 1985, and four times higher among those born between 1981 and 1989, than among people born in the 1940s, based on national U.S. population data.

The conclusions are drawn from the nearly 4,900 adults who were diagnosed with appendix cancer in the United States between 1975 and 2019.

The pattern of increasing cancer rates held true, to varying degrees, for all tumor types, including nonmucinous, mucinous, goblet cell, or signet ring cell carcinoma, the researchers said.

Rates of colon cancers and other gastrointestinal malignancies have also been rising in younger adults, for reasons that remain unclear, the researchers noted.

“It really struck our curiosity... Would we observe similar patterns in rare appendix cancers?" said study leader Dr. Andreana Holowatyj of Vanderbilt University Medical Center in Nashville, Tennessee. "And certainly the answer was yes,”

“The big question remains as to why is this happening,” she added. “But what's most important is that as these higher risk birth cohorts continue to age, it's likely these rates will continue to increase.”

In a separate study reported at a recent meeting of cancer doctors, Holowatyj and colleagues found that patients with appendix cancer generally experienced several months of abdominal pain, bloating, and pelvic pain before diagnosis.