Some formulations of the go-to antibiotic amoxicillin are hard to come by this fall in the U.S., Canada, and parts of Europe, with recent shortages also reported in Ireland, Malaysia, Romania, and Australia. While antibiotics treat bacterial infections, some clinicians prescribe them anyway for patients with viral illnesses, a slew of which are surging in North America and globally this fall. That could mean amoxicillin isn’t always available to those who truly need it, like children with ear and sinus infections or bacterial pneumonia, experts say.

Antibiotics have always been overprescribed, and supply-chain issues—coupled with high demand this fall—have created the perfect storm, Dr. Georges Benjamin, executive director of the American Public Health Association, told Fortune.

“Unfortunately, just as we’re going through peak cold and flu season, two of the drugs most commonly used for those, there seems to be a shortage,” he said, referencing amoxicillin and Tamiflu, an antiviral used to treat patients with the flu. The U.S., Canada, and parts of Europe are also seeing a shortage of acetaminophen (Tylenol) and ibuprofen (Advil) for children as a result of tripledemic-driven demand.

If you or your child has a regular medical provider, they likely have a good sense of  your history and needs. When your child gets a cold virus, perhaps they always get an ear infection that resolves only with antibiotics like amoxicillin, Benjamin said.

“But if you go into urgent care or where someone who doesn’t know the patient is treating them, they’re going to err on the side of it being bacterial,” he said, adding they will likely treat it with antibiotics, he said.

In some cases, the shortage is leading doctors with no other choice but to prescribe needy patients antibiotics that could be less than optimal and lead to antibiotic resistance, George Udeani, head of pharmacy practice at the Texas A&M Irma Rangel School of Pharmacy, recently told CIDRAP News.

Antibiotic resistance occurs when bacteria—not humans or animals—change in response to medications, rendering them ineffective. This could lead to a “post-antibiotic era, in which common infections and minor injuries can once again kill,” according to the World Health Organization.

If you or a loved one needs an antibiotic this fall, something will be available, Benjamin said. But it may not be your doctor’s first choice.

“Other antibiotics have more side effects,” he said.