When should a person with corn on his foot stop applying salicylic acid? or what are the sign of cure of corns on feet while using salicylic acid?

A corn is : Essentially dead skin accumulated secondary to friction. Acid burns the skin away. When you don't see the corn anymore then stop. I am nota fan of acid as it is easy to burn ones healthy skin so if you chose to do so, do it with caution. No diabetic should ever use acid.

Immediately: I don't advise anyone to ever use medicated corn pads. The "medication" is salicylic acid and i can't begin to count the painful burns I have treated from patients using it improperly. It does not discriminate corn from skin and will continue to burn whatever tissue it is applied to. Those chemical burns take forever to heal. See a podiatrist. They can trim the corn off in seconds.

Corns: Corns are caused by a hammer toe and enlarged bone under the corn. Salicylic acid does not cure corns. In fact salicylic acid can burn the skin. If there is a severe vascular problem or neuropathy, the acid can burn through the skin and create an open sore and eventually could expose bone in people who have lost nerve sensation. Professional care is recommended.