Ma'anar ƙamus na "rashin lafiya ta jiki" wani yanayi ne da tsarin garkuwar jikin mutum ya yi kuskure ya kai hari ga kyallen jikinsu ko gabobin jikinsa, wanda ke haifar da kumburi da lalacewa ga kyallen ko gabobin. A cikin cututtuka na autoimmune, tsarin rigakafi ya kasa gane antigens na kansa a matsayin "kai," kuma a maimakon haka yana ɗaukar su a matsayin mahara na kasashen waje waɗanda dole ne a kai hari kuma a lalata su. Wannan na iya haifar da bayyanar cututtuka da yawa da matsalolin kiwon lafiya, dangane da abin da kyallen takarda ko gabobin suka shafa. Misalan cututtuka na autoimmune sun haɗa da rheumatoid arthritis, lupus, sclerosis, da nau'in ciwon sukari na 1.