During an event commemorating Sept. 11, 2001 on Sunday, Democratic presidential candidate Hillary Clinton excused herself early after becoming "overheated." Mrs. Clinton's physician, Lisa Bardack, revealed that the candidate was dealing with pneumonia, which had been diagnosed on Friday.

Politically, the timing was not ideal. The revelation came as the Clinton campaign has been hit by a wave of conspiracy theories elevated by the Donald Trump campaign and his supporters about the candidate's health over the past few weeks, with many online theorists questioning whether Clinton was well enough to be president.

Is Clinton being held to a double standard because she is a woman?

For most presidential candidates throughout history, presidential health concerns have not seemed to concerned the public nearly as much as this election, raising questions about what makes this campaign different.

A recent report from NBC News on Clinton's health posed the question of why Clinton's diagnosis was hidden until hours after her Sunday near-collapse and wondered if Clinton would "accept the obligation to inform the public about her health." But for much of history, such an obligation did not exist.

According to Gallup, many presidents have maintained silence on their respective health problems. Woodrow Wilson had a stroke in office, Ronald Reagan underwent secret surgeries, and Franklin Delano Roosevelt famously went to great lengths to give the public the impression that he was fully mobile after his battle with polio even though he spent much of his life in a wheelchair. Grover Cleveland once disappeared from the White house for a full four days so that he could have a tumor removed on a yacht, away from prying reporters, according to NPR. John F. Kennedy "suffered from more ailments, was in far greater pain and was taking many more medications than the public knew at the time or biographers have since described," the New York Times reported in 2002.

And that's only to name a few.

These presidents all kept their physical ailments secret in order to project an image of strength and reliability to the public, a standard that was maintained through much of the history of the office until relatively recently. As candidates' lives have become increasingly open to scrutiny on the internet and various taboos in media about candidates' personal lives have been broken, it has become much more difficult for a candidate to hide an illness.

In response to increasing transparency, presidential candidates have begun to come forward with health problems early on in their campaigns, including Dick Cheney's heart issues and John Kerry's successful battle with prostate cancer before his campaign began, according to Gallup. At the time of the Mr. Kerry campaign, 92 percent of voters, both Republican and Democrat, said that they were not concerned about his ability to serve as president.

In contrast, Clinton's health has become an increasingly important issue for voters during this election. A Rasmussen Report survey from before Sept. 8 shows that 86 percent of likely voters say a candidate's health is important to their vote, with 43 percent who characterize candidate health as "Very Important." Some 17 percent of Democrats and 73 percent of GOP and unaffiliated voters said that Clinton's health was a legitimate concern for them. Those numbers could rise after news of Clinton's diagnosis.

While Clinton's desire to keep her health issues quiet is nothing new on the presidential front, the response from her opponents has proven intense. As a female candidate, she has proven more susceptible to accusations of "weakness" from Republican presidential nominee Donald Trump and his supporters, in contrast to Mr. Trump's "strongman" image. The Trump campaign has had a great deal of success in presenting the Republican candidate as a traditionally masculine figure that fights rather than compromises, representing his opponents as weaker and incapable of making the tough decisions necessary to run the country.

In contrast, Clinton's transparency about her health opens herself up to rhetorical attacks along this line.

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Even before her diagnosis became public, however, Clinton was already under attack for similar reasons, with many fringe conservative sites sharing fake medical records as "proof" that she does not have the physical strength to effectively lead the country, according to USA Today.

While Trump stands to benefit from Clinton's diagnosis, neither candidate has released a complete medical report to the public.