The U.S. defense secretary is facing scrutiny after failing to immediately disclose to the White House his recent prostate-cancer diagnosis and a related hospitalization, a breach of protocol for which he has apologized.

But while the secretary, Lloyd J. Austin III, as a cabinet member, faces certain expectations about what he must disclose publicly regarding his health, and when he should do it, mental health experts who work with patients who have serious illnesses, such as cancer, say that reticence is common — even in the era of oversharing online.

“I see it with my patients all the time,” said Dr. Andrew Esch, senior education adviser at the Center to Advance Palliative Care, a national health care advocacy organization based in New York City. “It’s very human to not want to have yourself sort of flayed open for the world to see.”

There are many reasons people might opt to keep their illness to themselves in certain contexts, experts said, but some are more common than others. Privacy can be a coping strategy, said Dr. Itai Danovitch, chairman of the department of psychiatry and behavioral neurosciences at Cedars-Sinai in Los Angeles, particularly in the early days following a diagnosis, when patients are deluged with new information.