The U.S. deep-poverty rate is 6.8 percent. In Camden, the rate of deep poverty is around three times that, at 20 percent, but its total population of about 72,000 is a fraction of Philadelphia's.
Philadelphia's overall poverty rate stands at 26 percent, figures show.
The rates of poverty and deep poverty in Philadelphia remained statistically the same between 2013 and 2014, figures show.
Most Americans cannot fathom the level of privation that deep poverty represents, experts say.
"It means we have so many people with a long way to reach any semblance of stability," said Kathy Fisher, policy manager at the Greater Philadelphia Coalition Against Hunger.
Miring people in deep poverty are overwhelming challenges that prevent them from consistently earning an income, Fisher said, including health problems and low literacy.
Living in deep poverty differs from merely being poor, said Judith Levine, a sociology professor at Temple University.
"Many people move in and out of poverty because of short-term setbacks like job loss or divorce," Levine said.
But people in deep poverty are stuck for long periods of time, and that has terrible consequences for their children, she added.
A significant number of the children from deeply impoverished families grow up to have severe depression and suicidal thoughts, studies show.
Ultimately, Levine said, "the stress of deep poverty is not knowing how you'll survive. So, survival becomes your job. It's relentless, day in, day out."
Many but not most in deep poverty are homeless, experts say. The majority double or triple up with friends or family members, or live in other tenuous arrangements, experts say.
"It's bleak," Levine said. "And it's hard for the rest of us to understand it's happening right around us."
The number of Philadelphians in deep poverty is greater than the total populations of cities such as Syracuse, N.Y.; Dayton, Ohio; or Berkeley, Calif., federal figures show.
Why Philadelphia leads in poverty is hard to pin down, though economist Neeta Fogg of Drexel University said it seems the city has a greater fraction of its population detached from the labor market than do many other cities.
This is not merely unemployment, but a permanent lack of participation in the job market because of low educational attainment and an inadequate number of jobs, Fogg said.
Experts say Philadelphia's poverty affects the city as a whole: A poor and uneducated workforce dissuades businesses from settling here.
Deep poverty increased nationwide after 1996, when the welfare system was changed, experts say. The number of people on cash welfare was drastically reduced, and the amount of time people could receive benefits was limited.
The hope was to get people into jobs, and it worked during more prosperous times, said Sheldon Danziger, president of the New York-based Russell Sage Foundation, which conducts social-science research.
But the United States has undergone eight years of "very difficult labor markets," Danziger said, and that means people who would have had welfare to raise them out of deep poverty in the past don't have that chance now.
There is little in the federal safety net to help those in deep poverty, said Jane Waldfogel, a poverty expert with Columbia University's School of Social Work.
"They may have food stamps, and if they're lucky, they can qualify for public housing," she said. "But for most in deep poverty, we haven't done much to reach them."
Among the "lucky," Angela Sutton, 39, a single mother of two children, ages 8 and 14, in Northeast Philadelphia, lives in subsidized housing.
Because of chronic pain she suffers from a gunshot wound to her abdomen as a child, it has been hard for her to find and keep work.
"Day to day, I try to babysit, do hair, do anything I can," said Sutton, whose disability and food-stamp benefits amount to about $10,000 - roughly half the $20,000 poverty rate for a family of three.
"The money runs out at the end of the month," she said. "These days, my big question is, 'Do I pay the electric bill, or do we eat?' "