what is hidradenitis suppurativa?

Hidradenitis Suppurativa (HS), also known as 'Acne Inversa', is a physically, psychologically, and socially disabling disease affecting inverse areas of the body (those places where there is skin-to-skin contact - armpits, groin, breasts, etc.), and where apocrine glands and hair follicles are found. It is non-contagious and recurrent; typically manifesting as a progression from single boil-like, pus-filled abscesses, or hard sebaceous lumps, to painful, deep-seated, often inflamed clusters of lesions with chronic seepage (suppuration --- hence the name) involving significant scarring.
Abscesses may be as large as baseballs in some people, are extremely painful to the touch and may persist for years with occasional to frequent periods of inflammation, culminating in drainage, often leaving open wounds that will not heal. These "flare-ups" are often triggered by stress, hormonal changes, or humid heat. Drainage of the lumps provides some relief from severe, often debilitating, pressure pain; however, pain occurs 24 hours a day, 7 days a week for HS sufferers during flare-ups, and is difficult to manage.
Persistent lesions may lead to the formation of sinus tracts, or tunnels connecting the abscesses under the skin. At this stage, complete healing is usually not possible, and progression of the disease in the area is inevitable. Occurrences of bacterial infections and cellulites (deep tissue inflammation) are likely at these sites.
Because of the drainage which may have a foul odor, fever and fatigue caused by acute inflammation and the physical restrictions caused by pain and skin deformation, people often cannot work, drive, exercise or even perform day-to-day tasks, and are ashamed to go out in public. HS sufferers may go through severe bouts of depression, avoid public and inter-personal contact, become sedentary and often overweight.
HS typically goes undiagnosed for years because patients are ashamed to speak with anyone. When they do see a doctor, the disease is frequently misdiagnosed. Only relatively few physicians are able to recognize it and even when they do, suggested treatments are often ineffective, temporary and sometimes even harmful. There is no known cure nor any consistently effective treatment; what works for one person may not work for another. In advanced, chronic cases, surgery is often the choice, but recurrences of HS are not uncommon.
The mechanisms of the disease are described in this article.
Historically, HS has been considered a rare disorder, because it is difficult to accurately estimate the number of HS victims; they conceal their condition, even from friends and close relatives. Estimates, however, indicate at least 1 million - potentially up to 12 million - Hidradenitis Suppurativa sufferers in the United States alone!