https://www.independent.ie/life/health-wellbeing/curse-of-big-boils-how-karl-marx-had-a-pain-in-his-bum-34876314.html

Karl Marx suffered from abscesses all over his body, but particularly badly affected were his backside, his groin and under his armpits, which he himself described as 'a mess'. Painful lumps on his inner thigh would grind against his trousers, making even a short walk very difficult. Sitting was often impossible because of the carbuncles on his bottom. A large boil beneath the shoulder blade would make lying down quite an ordeal. In particularly black moods, Marx would hack at them with a cut-throat razor. Understandable, but not medically recommended. He lived in London for most of his adult life and all his doctor could do was recommend serious poisons that were once prescribed frequently for skin diseases. In the summer months, his physician would send him on bathing holidays to Margate for the 'sea cure' together with a prescription for arsenic three times a day. Marx felt that arsenic dulled his mind. It probably did a lot more besides. In dark days, and there were many, he would blame bourgeoisie 'swine' for his carbuncles. Modern thinking is that Marx suffered from a severe form of hidradenitis suppuritiva (sometimes abbreviated to HS). This is a relatively rare condition of the sweat glands that causes clusters of pus-filled abscesses, often in the nether regions where sweat glands proliferate. The Irish Skin Foundation has an excellent section about HS on its website.