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Hidradenitis suppurativa (HS) was first described in the 1800s. It was originally thought to be an infection of glandular structures, primarily because it was noted to produce pus and because it occurred in crease areas of the body, regions rich in the number of apocrine glands. Since then, it has been realized that neither infection, nor glands are causes, but that it is caused by irregular events within the hair follicles. It may affect 1-4% of the population and is 3 times were likely to occur in women than men.  It has also been referred to medically as “acne inversa”.


A number of clinical features define HS.  First is the presence of one or more inflammatory nodules (or “boils”), usually occurring in crease areas.  Unlike boils caused by infections, these usually occur, heal and then recur in the exact same area.  They may also extend to regions nearby, forming tunnels or sinus tracts.  Characteristic is the situation where one can press on one spot, and drain from a different one through these tunnels.  Preferred areas are the underarms, groin, low abdomen, buttocks, and the area around the rectum.  Underarm, groin and under-breast areas are somewhat more common in women, while the buttock and perianal areas are more frequently affected in males. 

Another common feature of HS is its association with other problems arising in follicles: acne, boils in the scalp, and pilonidal sinus/cyst.  In our experience, a little over 50% of persons will have a history of acne significant enough to require treatment.  It may affect the face or back.  Men are more likely to have had severe acne than women. Like acne, HS generally appears only after adult hormones begin, and may flare for many women premenstrually.  Also like acne, hormone levels are usually normal.  Boils in the scalp (folliculitis decalvans/dissecting cellulitis of the scalp) is the least common of the associations, occurring in about 6% of HS patients; however it may be severe enough to cause scars and hair loss.  Pilonidal sinus or cyst is a dimple or boil usually found at the base of the spine/between the buttocks.  It may periodically drain and be painful.   It is seen in about 36% of patients with HS and is also more common in men.  On a milder note, many patients will have non-inflamed areas where several blackhead-like structures will join in a single pore.   Finally, almost 30% of patients with HS will have someone else in the family who has also had “boils”.

There are other medical conditions which have been noted to occur more often than expected in patients with HS.  Joint inflammation including features similar to that seen in rheumatoid arthritis, systemic lupus erythematosis, and Sjogren’s syndrome may occur.  Other inflammatory conditions including Sweet’s syndrome and pyoderma gangrenosum have also been seen with HS.  In some instances, successful treatment of HS has resulted in significant improvement in these other conditions, further suggesting a medical relationship between them.


HS is not caused by infection, bad hygiene, abnormal hormones, race, or diet.  However, it may be aggravated by excessive size/overweight, smoking, and possibly by certain medications (such as lithium) or foods.

Current evidence suggests that the (normal) hormones of the patient travel through the blood system to a point on the surface of a gland which is part of the follicle or pore. At the gland, there is a recognition point which is activated by the hormone. This turns on the pore to grow and produce moisturizing oils. These oils would normally travel to the surface, lubricating the skin. In HS, the moisturizing oils are released through a rupture from the pore into the surrounding skin, probably as part of a weakness at a key point in the structure of the pore. This lubricating material causes a localized response producing inflammation – the boil. A further feature is the seeding of repair cells (epithelial stem cells) into the tissue around the pore; these are thought to lead to the development of the sinus tracts or tunnels that connect one boil to another.


There is no specific test for HS.  Diagnosis is based on the physical findings noted.  Although certain families with HS have been found to have common gene findings, these tests are not generally available or relevant.  Because HS can become infected, cultures of the drainage may occasionally be necessary.  Additionally, since hormonal imbalances can aggravate both acne and HS, testing for hormone levels may also be indicated.


It has been recognized that in order to determine ideal therapies, it is important to compare severities of the condition.  One system geared to that goal is the Hurley Grading System.  In this ranking, Grade I represents patients with a single or multiple persistent or recurring abscess without tunnels or scars..  Grade II includes patients with one or more areas of involvement in which there is tract formation and associated scars.   Grade III includes patients with multiple areas with multiple interconnected tunnels/sinus tracts and scars.

An additional grading system was proposed by Sartorius, in which a numerical value is assigned for each of the features of the condition: number of areas with boils, scars, tunnels, distance between lesions.  Each of these systems have been helpful in determining the degree of improvement with the various therapies used.