8th June 2025

Cause

The aetiology is not fully understood, but proposed contributors and associations include:

• Immune factors – immune system activation from occluded hair follicles forming painful nodules and abscess rupture leading to sinus tracts, scarring and tissues destruction; complex interactions with the skin microbiome.
• Genetics – family history is seen in 30% of cases.
• Hormones – clearly more common in women in Western populations but this may not be reflected elsewhere; can vary with menstrual cycle and pregnancy.
• Smoking – thought to be due to hair follicles being more likely to be blocked.
• Obesity – friction and sweating in skin folds with hormonal and pro-inflammatory changes may promote HS. 
• Other diseases – co-existing metabolic syndrome, type 2 diabetes mellitus, atherosclerosis, spondyloarthropathy, inflammatory bowel disease, depression and cardiovascular disease commonly seen. Can be part of a rare autoinflammatory syndrome, e.g. PASH (pyoderma gangrenosum, acne, suppurative hidradenitis), PAPASH (pyogenic arthritis, pyoderma gangrenosum, acne, suppurative hidradenitis).