Trench foot or fat foot is a medical condition that is caused by keeping feet in the cold, in dirty places, or in water for a long time. Trench foot was a big problem in the trenches of World War I. Many of the soldiers fighting got this condition.
The soldiers found it difficult to cope with the swelling wearing their boots but after realised that they couldn't get the boot on again as the foot had swollen to twice its size. Many men who suffered from it ending up having their feet amputated because they couldn't deal with the pain.
This can be treated by rubbing it to cause friction and if it is kept warm it can heal itself.