WASHINGTON, May 13 (UPI) -- The presidential election's protracted primary campaign battle strains and exposes those who want to be the United States' next leader, observers say.

The toll has been perhaps greatest on Democrats Barack Obama

and Hillary Clinton, who have been battling for their party's presidential nomination, The Baltimore Sun reported Tuesday.

"For candidates, campaigning is like living in a giant petri dish full of germs, shaking thousands of hands of people who have been blowing or picking their noses, changing wet or dirty diapers or scratching God knows what," said Charles E. Cook Jr., publisher of The Cook Political Report. "It's a wonder that they live through it."

Obama and Clinton both use hand sanitizer, while former presidential contender and New Mexico Gov. Bill Richardson, is among those who still refuse to use the gel disinfectant, contending its use is condescending to voters.

But no matter the health precautions, the candidates still feel the stress of the campaign trail, the political publication said.

"I think it's pretty clear this kind of schedule is a strain on the body; not all that different from what we might see in people working three jobs or switching rapidly between the night shift and the day shift," said Dr. Lawrence Cheskin, director of the Johns Hopkins Weight Management Center. "