The search for the cause of HS has been difficult. Suggested causes include:
- Hormones/hormone imbalance,
- Local factors including heat and humidity, sweating, rubbing of skin-to-skin,
- a reaction to deodorants or other topical chemicals,
- Abnormal inflammatory responses to follicle rupture,
- Abnormal responses to normal bacteria in the skin,
- Abnormal healing responses to follicular injury,
- Heredity, and
- Abnormal control of growth factors within the follicle/pore.
The sequence of events involved in the cause of HS is generally thought to be as follows:
Hormones travel through the blood where they are recognized by ‘receptors’ in the follicular part of the pore and the sebaceous (oil) gland.
The receptors stimulate the production of the normal skin surface cells (keratinocytes) cells that line the inside of the follicular structure. They also turn on the sebaceous glands to “lubricate” the skin surface.
The manufactured lining cells fail to separate from each other and form a compact obstruction that prevents their normal transit to the surface. Their continuing production, caused by the hormones, results in an expansion of the follicle. This ruptures the follicle at its weakest point.
The ruptured pore materials, consisting of keratinocytes (lining cells), residual hairs, broken parts of the follicle wall, fatty acids, bacteria and yeasts – all interact in the dermis (the part of the skin under the surface surrounding the follicle) with the two immune systems and this leads to severe inflammation: pimples, and boils.
The skin attempts to heal the broken follicle but if it cannot do so the inflammation spreads under the skin surface, there are further attempts to heal and failure leads to creation of tunnels, the creation of an invasive gelatinous mass, and eventually the area heals by scarring.
Many features are similar to acne: It usually begins in early adulthood, may be flared during hormonal cycling or hormone excess, is likely triggered by diet, tends to occur in families, produces lesions similar to acne, and begins within the pore. In addition, three other follicle-related diseases are known to occur more frequently in patients with HS: Acne (roughly 50% of HS patients), Pilonidal cyst – a cystic/boil-like process just below the tailbone (roughly 35% of HS patients), and Folliculitis Decalvans/dissecting cellulitis of the scalp – boils in the scalp (roughly 6-8% of HS patients).
At least 30% of patients may have someone else in the family diagnosed with HS, or described as having a history of “boils”. Frequently, no diagnosis of HS was made. With improving awareness of the condition, many more patients, and their relatives, are being identified to have, or have had, the disease. This has allowed further investigation of the genetic aspects leading to the HS events. Some affected members of families with HS have been identified to have abnormalities in the genes which control events within the follicle, especially surrounding the gamma secretase gene pathway. Although this information appears to give new insight into the cause, the full step-by-step process is only partially understood.