Foamy urine can be a sign of something serious—most notably, protein in the urine, a condition called proteinuria. Normally, your kidneys filter out waste while keeping important substances like protein in your body. But when they're not working properly, they may let protein leak into your urine. This can cause it to appear foamy or bubbly. Proteinuria can result from kidney-specific diseases like diabetes or lupus, but it may also indicate problems affecting other parts of the body. If you con