"And the magicians could not stand before Moses because of the boil" (Exodus 9:11). With each and every plague they kept adding [to their own affliction]: they put their hands into their bosoms and drew them out leprous as snow, and they were not healed until the day of their death. And so with each and every plague they kept adding [further harm to themselves], until the boil, as it is written, "And the magicians could not stand."
The Magicians Could Not Stand Before Moses
Yalkut Shimoni on Torah 184:2
(שמות ט יא) וְלֹא יָכְלוּ הַחַרְטֻמִּים לַעֲמֹד לִפְנֵי מֹשֶׁה מִפְּנֵי הַשְּׁחִין. כָּל מַכָּה וּמַכָּה הָיוּ מוֹסִיפִין, הִנִּיחוּ יְדֵיהֶם לְחֵיקָם וְהוֹצִיאוּם מְצֹרַעַת כַּשֶּׁלֶג, וְלֹא נִתְרַפְּאוּ עַד יוֹם מוֹתָן. וְכֵן כָּל מַכָּה וּמַכָּה הָיוּ מוֹסִיפִין (עַד יוֹם מוֹתָן, וְכֵן כָּל מַכָּה וּמַכָּה הָיוּ מוֹסִיפִין מַכָּה), עַד שְׁחִין, דִּכְתִיב וְלֹא יָכְלוּ הַחַרְטֻמִּים.