If you (or your patients) notice swelling in an arm, leg, or elsewhere, the first question is usually what’s causing it? Two common—but very different—culprits are pitting edema and lymphedema. They can look similar at first glance, especially early on, but their causes, clinical clues, and best treatments diverge. Getting the distinction right prevents delays in care, unnecessary tests, and the wrong therapies. This guide breaks down the differences clearly, shows how clinicians tell them apart, and offers practical next steps—including when to seek urgent care and how to find a certified lymphedema therapist.