What it means: When the very tips of the toes swell to the point where they lose their usual angle and appear to bump upward at the ends, it's called "digital clubbing" or "Hippocratic clubbing" after Hippocrates, who described the phenomenon 2,000 years ago. It's a common sign of serious pulmonary (lung) disease, including pulmonary fibrosis and lung cancer. Heart disease and certain gastrointestinal diseases, such as Crohn's disease, are also associated with clubbing.
More clues: Fingers can be clubbed as well as toes. It can happen in just some digits, or in all.
What to do: Treatment depends on the underlying cause, so report this serious symptom to a doctor. (Physicians are also well trained to look for clubbed digits during exams.)