Corns are calluses are hard thickened layer of skin that develops due to a protective response from repeated friction or abnormal pressure point. It can be found on top or between the toes, on the bottom of heel and ball of toes. The surface layer of the skin thickens and builds up by hyper keratinisation causes irritation of the tissues underneath. These can be hard or soft. Hard corns are usually located on the top of the toe or on the side of the small toe.  Soft corns resemble open sores and develop between the toes as they rub against each other

Corns and calluses looks similar but there salient differences that distinguishes them. Corns are usually small, rounded with hard centre and inflamed margin. It usually develops on upper surface where foot does not bare weight. Corns are usually painful. Whereas calluses are broader flat thickened skin developed on weight baring surface; sole of foot. They are rarely painful.

It happens due to the normal defence mechanism of skin to protect itself from repeated friction or abnormal pressure. Common factors that causes formation of corns and calluses are-

1. Improper foot wear like tight or small shoe causes abnormal friction over curled up toes and very high heel puts abnormal pressure on ball of the toes. Use of shoes without socks or hard socks also causes corn and calluses formation 
2. Foot deformity causes abnormal bony prominence which exposes the skin overlying it to abnormal friction, pressure and weight transfer. Bunion, toe deformity, severe flat foot, high arch foot, rocker bottom foot and foot arch break down in Charcot foot. 
3. Abnormal gait causing deviation of sole contact and weight baring surface.

You may find a thickened hard skin, sometimes a rounded bump of skin over the bony prominence of a deformity like bunion, claw, hammer or mallet toe, between the toes, at ball of toe, heel or at any part of sole beneath a abnormal bony prominence. It may be painful and inflamed. If got infected then can have pus discharge. 

If you are a healthy then you may not to see a doctor for your corn and calluses. But you should see a doctor if you feel severe pain and difficulty in walking or wearing a foot wear, the area of corn or calluses become inflamed and there is discharge from it.  If you are a diabetic or have any peripheral vascular disease then you should visit a doctor with out any symptom. Because cracked skin of corn and calluses can cause a severe consequences of infection in these patient due to poor circulation of the skin.

To make a diagnosis of corn and calluses no special investigation is required. Local examination is confirmatory for diagnosis. But your doctor may examine your foot and gait and enquire about your foot ware choice to find any predisposing factor for corn and calluses formation.   

Selfcare and prevention:

• Soak your feet regularly in water and use a pumice stone or callus file to soften and reduce the size of corns and calluses.
• Wear a donut-shaped foam/silicone gel pad over the corn this will help to relieve the pressure. Use non-medicated corn pads; medicated pads may increase irritation and result in infection.
• Wear footwear that fit properly and have a roomy toe box.
• Apply moisturizer to keep the skin soft.

But one should not try to cut it by themselves as it can cause injury to surrounding skin and let an infection be happen. Specially the diabetic they should not even try salicylic acid lotion by themselves without consulting a specialist.

If your symptom is very severe or if you are a diabetic then your doctor may advice you:

• Offloading insole 
• Application of salicylic acid solution or gel
• Lesser excision 
• In severe painful cases surgical correction of associated deformity is recommended specially in diabetic patient surgical correction of deformity may require in asymptomatic corn and calluses also.

Similar skin lesion like corn or calluses

If there is no underlying predisposing factors are there and patient is not a diabetic then this type of skin lesion should be evaluated for skin wart and subcutaneous foreign body. Planter warts are caused by Human Papilloma virus entered the skin through a cut. It is painful and has a central black pigmentation. They usually appear at ball of toes and heel.