Those who are diabetic may develop diabetes-related neuropathy, a condition in which the nerves (most commonly in the feet) become damaged. This can lead to either extreme sensitivity or numbness in the feet.
For those experiencing increased foot sensitivity, even "soft" materials can become painful when in contact with the skin, especially if the foot moves against the material. This in turn causes extreme discomfort throughout the day.
Those with numbness or lack of sensitivity in the foot can develop sores, blisters, or other injuries unknowingly, which could lead to additional medical complications.