סימן ק סעיף כ

מִי שֶׁיֵּשׁ לוֹ מוּם בְּפָנָיו, בִּמְדִינוֹתֵינוּ שֶׁנּוֹהֲגִים שֶׁכָּל הַכֹּהֲנִים מְשַׁלְשְׁלִים אֶת הַטַּלִּיתִים עַל פְּנֵיהֶם, מֻתָּר לִשָּׂא אֶת כַּפָּיו. אֲבָל מִי שֶׁיֵּשׁ לוֹ מוּם בְּיָדָיו, כְּגוֹן שֶׁהֵן בַּהֲקָנִיּוֹת (פֵּרוּשׁ מִין נֶגַע לָבָן), אוֹ מְנֻמָּרוֹת בִּנְקֻדּוֹת דַקּוֹת, אוֹ שֶׁהֵן עֲקֻמּוֹת, אוֹ שֶׁאֵינוֹ יָכוֹל לְחַלֵּק אֶת אֶצְבְּעוֹתָיו, לֹא יִשָּׂא אֶת כַּפָּיו מִפְּנֵי שֶׁהָעָם יִסְתַּכְּלוּ בוֹ וְיַסִּיחוּ דַּעְתָּם. וְאִם הוּא רָגִיל בְּעִירוֹ, שֶׁכְּבָר שָׁהָה שָׁם שְׁלֹשִׁים יוֹם וּמַכִּירִים אוֹתוֹ, נוֹשֵׂא אֶת כַּפָּיו. הָיוּ יָדָיו צְבוּעוֹת, לֹא יִשָּׂא אֶת כַּפָּיו, מִפְּנֵי שֶׁהָעָם מִסְתַּכְּלִין בָּהֶם. וְאִם רֹב הָעִיר מְלַאכְתָּן בְּכָךְ, יִשָּׂא אֶת כַּפָּיו. מִי שֶׁאֵינוֹ יוֹדֵעַ לַחְתֹּךְ הָאוֹתִיּוֹת הֵיטֵב וְקוֹרֵא שִׁי"ן יְמָנִית כְּמוֹ שְׂמָאלִית, לֹא יִשָּׂא אֶת כַּפָּיו, אִם לֹא שֶׁכָּל הַקָּהָל קוֹרִין כֵּן. וְכָל כֹּהֵן שֶׁאֵינוֹ נוֹשֵׂא אֶת כַּפָּיו, יֵצֵא קֹדֶם רְצֵה מִבֵּית הַכְּנֶסֶת לַחוּץ, עַד שֶׁיִּגְמְרוּ נְשִׂיאַת כַּפָּיִם.

In our communities where it is customary for all kohanim to lower their tallisim over their faces, a kohein who has a blemish on his face, is permitted to pronounce the Birkas Kohanim. But a kohein who has a defect on his hands, like bahakaniyos, i.e. a white lesion, or they are speckled with small spots, or they are deformed, or he is unable to separate his fingers, may not bless the people,⁵¹Unless they follow the custom of covering their hands with their tallis. (Shulchan Aruch, Remah 128:31) because the people might look at him, and be distracted. If he is well-known in his town, having lived there for thirty days,⁵²Only if he intends to stay there for at least six months or so. But if he just happened to be there for thirty days, he may not go up. (Shulchan Aruch 128:30) and people recognize him, he may raise his hands to bless the people. If his hands are discolored from dye or paint, he may not raise his hands to bless the people because the people will look at them. If most of the people of the town follow this trade [of dyeing or painting], he is permitted to raise his hands in blessing. If he does not know how to pronounce the letters properly, or if he pronounces the letter shin like the letter sin, he may not raise his hands to bless the people, unless the entire congregation⁵³Radvaz, Maharit. See Mishnah Berurah 128:120, that if many people say it that way, he may duchan. pronounces it like that. Any kohein, who does not raise his hands for the Birkas Kohanim, should leave the synagogue before Retzeih is said, [and stay outside] until the end of the priestly blessing.⁵⁴In all these cases, if he went to the duchan, he need not step down. (Peri Chadash, also see Chayei Adam)

תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)