Liver disease:

Cirrhosis or liver dysfunction can disrupt fluid balance and result in leg and foot swelling.

Venous insufficiency:

As veins struggle to return blood to the heart, fluid can pool in the legs and feet.

Lymphatic system disorders:

Blocked or damaged lymph nodes can lead to lymphedema, leading to chronic swelling.

Infections:

Especially if one foot is swollen, painful, and red, it could be an indicator of cellulitis or another infection.

Medications:

Some drugs (e.g., steroids, blood pressure meds, antidepressants) can cause swelling as a side effect.

Pregnancy:

Fluid retention is common, especially in the third trimester, but excessive or sudden swelling can signal preeclampsia.