A rare condition that he somehow managed until he was set to earn 1 million a year. And the team was set to pay full cap.
Scott Powers did a lengthy article on it but Hossa's skin condition was actually eczema and it was triggered by his skin not being able to breath under his equipment. The condition got worse over time and the description of the impact in the story is quite gross, like bloody sheets and pus.
If you've known anyone with severe eczema, it's not a pretty sight. I've had mild eczema flare ups that required steroid cream treatment.
The issue for Hossa is that the meds to treat it got to the point where he was risking serious side effects and it was getting worse.
"The Cyclosporine reduced some of the itching and the symptoms, but it wasn’t perfect. It also complicated Hossa’s life in other ways. For one, Hossa had to take three pills in the morning and three at night.
The drug can be so dangerous the FDA has given it a black box warning. Some of the possible side effects include an increased risk of serious infections, higher blood pressure, kidney disease, tumor and skin cancer. Hossa went to Northwestern Memorial Hospital for testing every two weeks."
So at that point he decided it wasn't worth it. And Hossa is by no means the only person to have eczema outbreaks from hockey equipment. If you really want to get a sense of what he was dealing with search 'severe eczema' on Google images.
Incidentally the Blackhawks beat reporters didn't know about the condition but it explained certain behaviour like a lot of missed practices and even Hossa asking to do post practice interviews via phone.