The best answer is that Henry didn't just have ulcers - he suffered from a variety of ailments in his later years, of which the ulcers were one of the most visible symptoms. The most recent explanation for Henry VIII's medical woes is by Catrina Whitley (archaeologist) and Kyra Kramer (medical anthropologist). Their essay "A New Explanation for the Reproductive Woes and Midlife Decline of Henry VIII" (Historical Journal, 2010, pp. 827-848) covers the majority of Henry's late medical history, even though their stated aim is to explain his dynastic difficulties. The two main explanations offered are that he suffered type 2 diabetes - a diagnosis that is possible, but not necessarily the most like explanation for his ulcers. It would, however, explain the fact that the ulcers had difficulty healing, and his steady decline of health after becoming more obese as he aged.

The authors present the most likely candidate for his ulcer problems was osteomyelitis. Osteomyelitis is a bone infection, probably caused by a broken bone that failed to heal properly. Henry suffered several accidents while riding and jousting during his life. The most famous and severe came in January 1536, when Henry was practicing jousting (Scarsibrick states he was "running at the lists", which seems to be a practice joust against an opponent, rather than "running at the rings" which did not involve a second horseman) when he was unhorsed by his opponent. Henry remained unconscious for two hours before beginning to recover, causing a great deal of distress (especially to Anne Boleyn who miscarried in the days after receiving the shocking news). The ulcer would actually get better over time before getting worse again as his infection never was fully treated (though even if the diagnosis was known, there was not viable medical treatment in 1536x1547). Henry's infected thigh, along with his obesity and his decreased levels of activities likely all contributed to a chronic issue resulting in ulcers on his leg.