What Causes Hidradenitis Suppurativa (Acne Inversa)?

Painful red bumps that form in skin folds are characteristic of hidradenitis suppurativa.

Hidradenitis suppurativa, also called HS or acne inversa, is a progressive and chronic skin condition that causes painful, swollen red bumps to form on the body, often in skin folds or places where skin rubs together. The bumps can be extremely painful and disabling, and they may have a foul odor or drain pus or blood.

The main signs of hidradenitis suppurativa are painful, swollen red bumps.

• The bumps may drain pus or blood.
• These bumps may become infected.
• The bumps may have a foul odor.
• Bumps last a long time and worsen over time.
• The skin may harden and form scars around the bumps.
• Several bumps may form in one area and cause a small "tunnel" in the skin called a sinus tract.
• Common locations for the bumps are places where skin rubs together, including the following:
  • Armpits
  • Groin
  • Inner thighs
  • Buttocks
  • Around or near the anus
  • Under the breasts

Most of the time, the cause of hidradenitis suppurativa is unknown, but it seems to be a result of both genetic and environmental factors. The condition tends to run in families. It is not contagious, and poor hygiene does not cause hidradenitis suppurativa.

The bumps start with a blockage of hair follicles in body parts with a high concentration of sweat glands (apocrine glands), such as the armpits or groin. These blocked hair follicles trap bacteria (which causes pain, inflammation, and redness), and the follicles eventually rupture. The reason for this blockage is unknown.

Risk factors for hidradenitis suppurativa include the following:

• Obesity
• Smoking
• Crohn's disease (rare)

Medical professionals can make a diagnosis of hidradenitis suppurativa with a patient's history and physical exam. There are three criteria that need to be met for a diagnosis:

1. The lesions are typical:
   • They are painful red papules smaller than 1 cm in diameter or nodules larger than 1 cm in diameter.
   • Abscesses are painful and tender, and there is discharge from the papules or nodules.
   • Scarring (dermal contracture)
   • Double-ended acne papules (comedones)
2. Lesions have a characteristic distribution.
3. Lesions are recurrent (at least two recurrences over a period of 6 months).

In some cases, doctors may recommend the following lab tests:

• Complete blood cell count with differential and platelet counts (occasionally elevated white blood count)
• Erythrocyte sedimentation rate (ESR)
• C-reactive protein (CRP) assay
• Urinalysis
• Serum multiphasic analysis with determination of the serum iron level and serum protein electrophoresis
• Bacteriologic analysis, usually with a culture swab
• Immunochemistry for various cytokeratins and 6 desmosomal cadherins
• Histologic examination

An ultrasound of hair follicles and skin thickness may help reveal abnormalities deep within the follicle.

Hurley clinical staging of hidradenitis suppurativa is as follows:

• First stage: Solitary/multiple, isolated abscess formation without scarring or sinus tracts
• Second stage: Recurrent abscesses, single/multiple widely separated lesions, with sinus tract formation and cicatrization (scar formation at the site of a wound)
• Third stage: Diffuse/broad involvement or multiple interconnected sinus tracts/abscesses across the entire area

In the early stages, treatment for hidradenitis suppurativa may include some of the following conservative measures and lifestyle modifications:

• Shower daily and gently wash areas of HS with hands -- do not scrub or use a washcloth or loofah.
• Lose weight if overweight or obese.
• Stop smoking.
• Use ordinary soaps and antiseptic and antiperspirant agents (for example, 6.25% aluminum chloride hexahydrate in absolute ethanol).
• Apply warm compresses with sodium chloride solution or Burow's solution.
• Wear loose-fitting clothing on areas where HS is present.
• Get laser hair removal.

Medications that treat hidradenitis suppurativa include the following:

• Antibiotics
• Retinoids
• Corticosteroids
• Antiandrogens
• Immunosuppressants
• Estrogen derivatives
• 5-alpha-reductase inhibitors

Doctors may need to perform surgery once abscesses, fistulas, scars, and sinus tracts form. Non-ablative radiofrequency therapy may help patients in certain stages of the disease.

Complications of hidradenitis suppurativa include infections and in rare cases, sepsis, which is a life-threatening condition.