Just because one's physical pain isn't visible to others doesn't mean they aren't suffering. It's a lot like a judging a book by its cover: You have no idea what's really going on underneath just by looking at a person — especially while many out there are living with an invisible illness or disability.
For instance, there are those with fibromyalgia, who experience widespread pain and tenderness, affecting their ability to accomplish even the simplest of everyday tasks. And then you have mood disorders like depression, which can manifest itself in physical symptoms like headaches, muscle and back pain and fatigue.
Life with a chronic condition can be incredibly frustrating to those who suffer from them, and there are so many disabilities you can't see with the naked eye. From chronic fatigue syndrome and rheumatoid arthritis to Lyme disease and diabetes, here are 15 disabilities people suffer from every day that you can't tell they have by looking at them.
A version of this article was originally published in May 2015.