A callus is a “disease” of the skin.  Disease is in quotation marks because it is not really a skin disease but a normal reaction. A callus never occurs without a reason. Most of the time these occur in response to pressure and shear forces across the skin.  

The skin gets thick (keratin) that stays attached to the underlying dermis. This is the body’s response to try and protect the underlying tissue. They can get very thick and sometimes painful.

The callus can occur pretty much anywhere on the foot.  Some people get calluses around their heels. This is usually because they wear open shoes or go barefoot a lot. This puts a lot of shear force on the fat pad around the heel. A common place for calluses underneath the big toe joint. This is especially true if the patient has a bunion deformity. This is simply because there is increased pressure in that location and shear force when the patient is walking.

Also shoe gear plays a significant role in callus development .  Other common locations are centrally on the ball of the foot and underneath the 5th metatarsal head. Calluses can be aggravated by shoe gear that is too small or not very cushiony.

All these locations and 1 thing in common:  They have a bone underneath the skin that is putting undue pressure and shear force in that location. 

There are a few differences between corns and calluses that should help you identify which one you have for proper treatment.

Calluses are larger than corns and rarely painful. They’re flat areas of tough and thickened skin that appear in weight-bearing areas. They are your body’s way of protecting the inner layers of your skin.

Unlike calluses, corns have a core that points inward. They are conical in shape and are often surrounded by inflamed skin. As a result of the core pointing inward, they can press against nerves and cause pain, especially when you apply pressure on them. They often appear in non-weight bearing areas.

A corn is just a callus that occurs on the toes. Core insert called corns because they have a typical round appearance. They can occur between the toes or on top of toes depending on where the shear forces are occurring. Corns are usually caused by a small bone prominence on the toe itself. It is usually quite a well-defined small area.

A foot ulcer is an open sore on your foot. Your skin tissue breaks down, causing a hole in the deeper layers of your skin.

Ulcer size ranges from very small to larger than the size of a half-dollar. Foot ulcers can be crater-like and deepen the longer they are left untreated.

  In about 25% of patients with diabetes they developed neuropathy.  Neuropathy just means   “diseased nerve”.   If the neuropathy gets bad enough, the  patient can actually lose the ability to feel the feet enough to protect themselves from getting a wound underneath the callus.  A true diabetic foot ulcer almost always has a callus around it.  There is almost always a callus that occurs before the skin ulcerates.

Learn more: Diabetic Foot Ulcers

Any activity that increases friction on your foot can cause corns and calluses, but your chances of getting them to increase with age. Men and women over the age of 65 are often affected by corns and calluses.

Asides from friction, they might appear as symptoms of a more severe problem like hammertoes and bunions. If you continuously wear shoes that fit poorly — too tight or narrow, for example — corns and calluses will appear to protect your skin. The longer you keep those shoes on, the more buildup there will be.

Corns and calluses go away when you eliminate the cause of the friction and rubbing. If yours are caused by ill-fitting shoes, replacing those with more comfortable shoes or orthotics eventually alleviates the corn or callus.

However, if your corns or calluses are caused by a foot deformity like bunions, or if you have diabetes or poor circulation, you need to seek treatment from a doctor.