Hidradenitis suppurativa

http://www.aocd.org/skin/dermatologic_diseases/hidradenitis_suppu.html
http://www.mayoclinic.com/health/hidradenitis-suppurativa/ds00818

Hidradenitis Suppurativa

Hidradenitis suppurativa, also known as acne inversa, is a chronic, often debilitating disease primarily affecting the axillae, perineum, and inframammary regions. Prevalence rates of up to 4% have been estimated. Our understanding of the disease has changed over time. It is now considered a disease of follicular occlusion rather than an inflammatory or infectious process of the apocrine glands. Clinically, the disease often presents with tender subcutaneous nodules beginning around puberty. The nodules may spontaneously rupture or coalesce, forming painful, deep dermal abscesses. Eventually, fibrosis and the formation of extensive sinus tracts may result. The location of the lesions may lead to social embarrassment and the failure to seek medical treatment. Therapies in the past have consisted of long-term antibiotics, antiandrogens, and surgery. New treatments like tumor necrosis factor-alfa inhibitors have given clinicians more options against this difficult disease.

From: http://www.ncbi.nlm.nih.gov/pubmed/19293006

Corn a.k.a. hyperkeratosis, clavus, heloma and tyloma

http://www.epodiatry.com/corns-callus.htm
http://footcare.ygoy.com/foot-corns-and-corn-treatment/

The above mentioned websites are some reference if you are interested in a condition called foot corn. Well, it's basically, as suggested from the name, a corn-like lesion over the foot. To be accurate, it's hyperkeratosis. The function is nothing but to protect your feet from the hardship they are exposed to. Differentiation from it with that of a callus is important. Here is the difference: A callus generally refers to a more diffuse thickening of the skin (more common on the toes, but can occur under the ball of the foot) whereas a corn is a thicker more focal area area (more common on the toes). A corn can occur under and be surrounded by callus. Complication worried is that infection can occur on the it, and eventually leading to the formation of an abscess.