Callus is an area of thickened skin that forms as a response to repeated friction, pressure, or other irritation. Calluses are generally not harmful and help prevent blisters, as well as offering protection. However, excessive formation may sometimes lead to other problems, such as a skin ulceration or infection.

Treatment ― OTC Drugs
It is important to make sure it is not a wart.
#Salicylic acid, brush applicator [Duofilm]
#Salicylic acid, self-adhesive bandages
#Salicylic acid, tube application
#40% urea cream
  • Calluses are present on the left foot (plantar) and right foot (lateral).
  • Corns (calluses) occur symmetrically on both feet, where pressure is applied or where the shoe presses against the foot. If a similar lesion occurs in an area of no pressure, a wart should be suspected.
References Corns 29262147 
A corn, also known as a calvus, heloma, or focal intractable plantar hyperkeratosis, is a type of callosity. Corns are uncomfortable, thickened skin lesions that result from repeated mechanical trauma due to friction or pressure forces. In the literature, confusing terminology is often used to call different types of hyperkeratotic skin lesions. Nevertheless, a corn should be distinguished from a callus, which is a more diffuse type of callosity. Thus, a corn is a well-delimited focal area of hyperkeratosis. This condition is often seen in athletes and patients exposed to unequal friction force from footwear or gait problems, including the elderly, patients with diabetes, and amputees. It should be regarded as a symptom rather than an effective disease.
 Clavus 31536205 
A clavus or clavi (plural) is a frequently encountered condition in the out-patient clinic, known colloquially as a corn. It is one of the many hyperkeratotic lesions of the foot and therefore requires differentiation from other etiologies such as calluses or plantar warts. A clavus is a well-demarcated thickened area of the epidermis that has a central core. This skin lesion is most commonly found on the foot and is often painful. A clavus results from repeated friction, pressure, or trauma to a specific area of the foot. A callus is another hyperkeratotic skin lesion that is similar to a clavus. It is an area of thickened epidermis with less defined borders and is also the result of repeated mechanical stress. Additionally, calluses lack the painful central core seen with clavi. Calluses most commonly present on the hands and feet. The older and the physically active are most commonly affected by clavi. Treatment focuses on symptomatic relief and lifestyle modification to prevent future clavus formation. By treating this painful and sometimes life-altering skin lesion, physicians can have a profound impact on their patients’ lives.