• Upon leaving office, President Barack Obama seemed to be the latest victim of the expedited presidential aging process that has been known to plague presidents, causing them to appear to age faster because of the stress of the office.
  • Over the last 50 years, signs of aging have grown more noticeable as presidents are constantly photographed.
  • Side-by-side photographs capture presidents' changing faces from inauguration to their last day in the White House.
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  • As President Barack Obama reflected on his time in office, he had a way of acknowledging his waning time in the position: a joke about his graying hair.

    "Right now, we are waging war under authorities provided by Congress over 15 years ago — 15 years ago," he said in December 2016.

    "I had no gray hair 15 years ago."

    Indeed, despite his close-cut hairstyle, it was impossible not to notice the trademark presidential graying, as the president's short black hair became more of a salt-and-pepper color.

    And though some dermatologists maintain that Obama is the latest victim of the expedited presidential aging process, appearing to age faster because of the stress of the office, others say that it's more attributable to natural aging than stress.

    Other studies, including a comprehensive analysis of elections dating back to the 1700s, have found that heading a nation can take years off a leader's life. That analysis, from the Harvard Medical School, found that elected heads of government, on average, have lives almost three years shorter than those of the candidates they defeat.

    Here's how past US presidents have looked near the beginnings and ends of their respective terms.