Patients in the 21st century are pretty lucky. Medical science and technology have advanced so much that we can diagnose many thousands of distinct conditions, and we can even take genetic tests that scour our DNA for signs of a disease that may not materialize for decades — offering us a peek into our own future.

And with these advances, we are being diagnosed more and more. The number of people diagnosed with chronic health conditions and mental health disorders is at an all-time high — at least partly, most experts agree, because we have simply catalogued more diseases to catch.

Yet we are also increasingly anxious, anxious about our health — even anxious that we’re too anxious about our health. Our ability now to understand our bodies and put a name on what’s wrong with them does not always provide comfort; instead, it can create new fears and impose new constraints on us. Some health care leaders, including Donald Trump’s health secretary, Robert F. Kennedy Jr., argue that we are becoming over-medicalized — too ready to take a pill for something, just for the sake of taking something.

The reality is nuanced because medicine is, to put it mildly, complicated. But we should in fact be careful about doling out diagnoses, says Dr. Suzanne O’Sullivan, an Irish neurologist and the author of a new book, The Age of Diagnosis: How Our Obsession With Medical Labels Is Making Us Sicker.

In her book, O’Sullivan argues that our eagerness to diagnose, preemptively screen, and otherwise push these new tools to their limits is creating problems that deserve to be taken more seriously. She describes mutually reinforcing trends — the patient’s insistence on certainty and the doctor’s desire to avoid being blamed for missing something — that are driving clinical practice toward overdiagnosis. The phenomenon is even leading to more instances of doctors diagnosing certain cancers by 50 percent or more, due to the availability of new imaging tech that can detect even minuscule traces of abnormal cells.

Overdiagnosis can cause real harm. And so O’Sullivan advocates for “slow medicine,” in which doctors and patients take time to develop a relationship, monitor symptoms, and take a great deal of care before naming a condition — an approach that may sound quaint in an era of rapid-testing but something she says is actually more in tune with the reality that diagnosis is partly an art.

“Most diagnoses come with a huge amount of uncertainty. That covers asthma, diabetes, cancer, autism. Diagnosis is a clinical skill,” she told me in a recent interview. “Now, the difficulty, I think, with modern medicine is a lot of people don’t understand that and that they feel that the test — the blood test or the brain scan — makes the diagnosis, when actually a diagnosis is made on understanding the story in the context of the tests........

© Vox