One of the pillars of modern medicine is showing its cracks, according to a new report from the World Health Organization.

Antibiotics have turned once-deadly infections into minor inconveniences. They make lifesaving interventions, from surgery to chemotherapy, safer. But every time this powerful tool gets used, there's a risk -- antibiotic resistance.

Out of the billions of bacteria causing an infection in an individual, some small fraction may be naturally resistant to a given drug. Taking an antibiotic can clear the field for those resistant bacteria to spread.

"Antimicrobial resistance is just basic evolution," says Kevin Ikuta, an infectious disease physician and researcher at UCLA. He says we need antibiotics, but "we are in this battle we're trying to lose as slowly as possible anytime we treat an infection."

Humans are losing that battle faster than previously thought. In 2023, roughly 1 in 6 infections tested by labs worldwide were resistant to antibiotic treatment, according to WHO. The report says nearly 40% of antibiotics used to treat common urinary, gut, blood and sexually transmitted infections have lost effectiveness over the past five years.