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What is HS?


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 more 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 it's 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. Although HS can rarely be seen in children, it generally appears only after adult hormones begin, it may flare for many women premenstrually. 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. About 35% 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, tender nodules on the lower legs (erythema nodosum), inflammatory bowel disease (especially Crohn’s disease and ulcerative colitis), heavy body size, premature vascular disease (including heart attacks and strokes), opiate-dependency/pain management challenges, 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/excessive body weight, 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 oils.  These oils would normally travel to the surface, lubricating the skin.  In HS, the oils are trapped in the pore, causing the pore to rupture and releasing the irritating contents into the tissue around the pore.  Inflammation results.  A further feature is the seeding of repair cells (epithelial stem cells) into the tissue around the pore; these lead to the development of the sinus tracts or tunnels that connect one boil to another.

Insert paragraph 2 from “Grading of Hidradenitis” section


There is a great deal of information suggesting that genetic factors determine structural strength of pores.    A traditional theory suggests that pore/follicle weakness, combined with blockage in the outlet of the pore, ultimately leads to the rupture, and release of the contents into the tissue surrounding the follicle.  Additionally, dermatologic investigators continue to examine other features which may be responsible for causing the inflammation in HS.   The influences of bacteria continue to be debated as a cause, or aggravating, factor in HS.   In some patients, the “biofilm” – largely a balance of bacteria present in skin, may have a part in aggravating flares of inflammation in the disease.   Overall, however, it seems reasonable to conclude that the disease may have a strong genetic defect in the integrity of the pore, and that many factors may aggravate the abnormal follicle.   Observed triggers in the condition have included infection, body size, smoking, local skin environmental conditions, stress, hormonal abnormalities, and certain medications.


There are no specific blood tests to establish a diagnosis of HS. The diagnosis rests on the physical findings of recurring boils, scarring and tunneling in the skin.   Pores, with multiple black-heads going into a single pore, is also common.

Laboratory abnormalities, while non-specific, are common in HS. Measurements of inflammation are the hallmark of the condition, and usually correlate with the severity of the HS. Hormonal imbalances of hormones (as seen with polycystic ovaries) or adrenal gland overactivity, thyroid problems and diabetes are frequently discovered. Blood problems, including anemia, and elevated platelets may also occur. These findings underscore the need for thorough physical and laboratory evaluation in virtually all patients with HS.


The most commonly-used system for “grading” the severity of HS is the Hurley system. Grade/Stage I is the findings of recurring boils, but without scarring or tunnel formation (these are also called sinus tracts). Hurley Stage II is the setting where there are recurring boils, but with limited scars and/or sinus tracts. Hurley Stage III describes the setting where there are recurring boils, but with more extensive scars and sinus tracts, often involving the entire anatomic area (for example, the entire underarm).

Other grading systems have also been proposed, sometimes using patient symptoms or functional properties. We have developed our own scoring system, the Hidradenitis Suppurativa Index, which incorporates each of these features: physical findings, symptoms, and daily capabilities – into a single score. In that way, we can truly track the progress of the condition, and evaluate it’s treatment response.

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