When your skin becomes thick and hard inresponse to friction, pressure or irritation, this toughened skin is known as callus, and corns are actually special shaped callus of dead skin which occurs on hairless and smooth skin surfaces like soles and palms.
Knife callus develops in experienced cooks at base of index finger, initially blister may be formed before callus formation. Similarly a callus is also found on forehead of Muslims, which is known as zabiba/zebiba/zebibah or Prayer Scar or prayer bump. In extreme cases, the callus can becomes very thick to create a real bump that protrudes from the forehead
Many people who do wear uncomfortable shoes develop these corns at sole of feet or between toes, these corns develop due to intermittent pressure over a particular area of sole of feet, actually under pressure hyperkeratinisation of skin takes place which gets surrounded by a hard nodule at the centre.
Patients feels severe pain on walking, they may range from single to multiple in numbers, they are actually CONE shaped with narrow part embedded inside, soft corns are found to occur on toes, while hard ones on sole of feet.
Scientific name of corn is heloma, hard cone is known as heloma durum and soft corn is called as heloma mole.
Treatment is actually surgical excision of corns under local anaesthesia.
Note: you have to excise it in form of CONE otherwise if any part is left it will reoccur, so you need to excise it completely, when skin starts bleeding, that means you have excised it completely, sometimes it has been found that it bleeds a lot while excising, so you need to provide pressure bandage. What I have written is my personal experience so you must follow it..
Corns can be very dangerous in diabetic patients as they can cause diabetic foot.