Your feet are severely cracking, scaling, or peeling.
There are blisters on your feet.
There are signs of bacterial infection, including:
Increased pain, swelling, redness, tenderness, or heat.
Red streaks extending from the affected area.
Discharge of pus.
Fever of 100°F(37.78°C) or higher with no other cause.
Symptoms that do not improve after two weeks of treatment with a non-prescription product.
Spreading of the infection to other areas, such as the nail bed, or skin under the nail, the nail itself, or the surrounding skin.
Your toenail is getting thicker and causing you discomfort.
You have heel pain accompanied by a fever, redness (sometimes warmth) or numbness or tingling in your heel, or persistent pain without putting any weight or pressure on your heel, or the pain is not alleviated by ice, aspirin, (or ibuprofen or acetaminophen).
You have diabetes or certain diseases associated with poor circulation and you develop athlete's foot. People with diabetes are at increased risk for a severe bacterial infection of the foot and leg if they have athlete's foot.