A corn can be of two types. A Heloma durum (hard corn) or it can be a Heloma molle (soft corn). They are similar in nature, although typically appear at different location which allows different firmness to the lesion.
Symptoms of corn is a thickening of skin over a pressure area on or between the toes. This is occasionally painful, it can become red and swollen as well. Relief of symptoms is obtained when pressure is not applied to these areas, for example, removing your shoes.
Causes of corns are due to structural bone deformities, most commonly hammertoes The contracture of the toe at one of its joints create a bone pressure. The skin then gets trapped between the bone and your shoes causing a friction. In response your body through inflammatory processes form a more protective skin barrier, being thicker skin. The hard corn forms on the tops of the toes, whereas the soft corn forms between the toes. The bones between two digits can also rub together causing this friction on the skin, but since it is one toe rubbing the other, the tissue remains moist and forms a very soft corn.
Prevention is by controlling your foot structure before this thick skin develops. Wear good supportive shoes or arch supports if needed. Pay attention to early signs of friction like blister formation. This tells you where the areas that are more likely to cause a corn. Corns can become serious if they lead to an ulcer and further infection.
Diagnosis is first by clinical suspicion of symptoms. Typically in your podiatrist office x-rays will be taken to exam the foot structure and bone deformities. The corn is usually not a diagnosis, but rather a symptom of the underlying cause, for instance a hammertoe, or bony exostosis.
Podiatric Care may include trimming the corn using a blade or special tools. Strapping or padding techinques maybe used to temporarily re-align the toes to decrease the pressure areas. Most of these measures though provide relief temporarily unless the bone problem is addressed. A modification in shoewear or orthotics may be used to control your foot structure for a more permanent relief.