The Prophet [SAW] used to say: "Allahumma inni a'udhu bika minal-jununi wal-jadhami, wal-barasi wa sayy'il-asqam (O Allah, I seek refuge in You from possession, leprosy, leukederma and bad sickness (that may lead to visible deformity)."  

أَنَّ النَّبِيَّ ﷺ كَانَ يَقُولُ اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْجُنُونِ وَالْجُذَامِ وَالْبَرَصِ وَسَيِّيءِ الأَسْقَامِ