When can tissues become edematous (swollen)?

Many causes: Tissue that is inflamed (infection, immunity, injury) leaks protein-rich fluid into the interstitial spaces. Increased pressure in the veins (a rubber band around a finger, running when you're out of shape), low serum albumin, or fluid overload in kidney failure, and plugged lymphatics are the other causes. Edema's a key feature in everything from a mosquito bite to severe heart failure.