According to the different pathophysiological mechanisms, cutaneous EIMs are divided into the following four categories: (1) specific skin manifestations with the same histological features as IBD, such as metastatic CD; (2) reactive skin manifestations with similar pathophysiological mechanisms to IBD, such as PG, Sweet’s syndrome, EN, and aphthous ulcer; (3) IBD-related skin diseases, such as psoriasis, hidradenitis suppurativa, and atopic dermatitis, and (4) IBD-treatment-induced skin lesions, such as anti-tumor necrosis factor (TNF)-α-induced skin eruptions (10). The gene discussed is TNF; the disease is hidradenitis suppurativa.