We’ve all experienced it: a little bit of swelling in our feet after a long day on our feet, a transatlantic flight, or a particularly hot afternoon.

In these cases, the swelling is usually temporary, harmless, and goes away with a little rest and elevation.

But what if the swelling is persistent, appears suddenly, or is accompanied by other worrying symptoms?

Swollen feet, a condition known as edema, can be a subtle but serious sign that something is not right within your body.

Ignoring it can mean missing a crucial early warning signal for conditions ranging from heart failure to kidney disease.

Taking a moment to check for these nine warning signs could be the most important thing you do for your health today.

The Nine Warning Signs

1. Swelling in One Leg Only

If you notice that one of your legs is significantly more swollen than the other, especially with an accompanying feeling of warmth, redness, or pain, do not ignore it. This is a classic symptom of a deep vein thrombosis (DVT), a blood clot that forms in a deep vein, usually in the leg. If this clot breaks free and travels to the lungs, it can cause a life-threatening pulmonary embolism. Seek immediate medical attention.

2. Swelling with Chest Pain or Shortness of Breath

This is a medical emergency. Swelling in the feet and ankles combined with chest pain, difficulty breathing, or dizziness could indicate a serious problem with your heart or lungs. It may be a sign of congestive heart failure (where the heart can’t pump blood effectively, causing fluid to back up) or a pulmonary embolism (a blood clot in the lungs). Call for emergency services immediately.