Halakhah su Levitico 21:18

That He prohibited a priest that has immersed on that day (tevul yom) from serving [in the Temple] - even though he has has purified himself - until [that evening]. And that is His saying about the priests, "and not desecrate the name of their God" (Leviticus 21:18). And one who transgresses this negative commandment is liable for death at the hands of the Heavens. Yet a clear verse did not appear about it, but it has rather been passed down. [...] And in Chapter 9 of Sanhedrin (Sanhedrin 83b), they said in the explanation, "'They shall be sacred to their God and they shall not desecrate the name of their God' (Leviticus 21:6). If [this verse] is not written with regard to the matter of an impure priest who performed the service, [as that has already been explained,] then apply it to the matter of a priest who immersed that day who served. And it learns it out from [a verbal analogy of the word,] desecration [in both places]." And they listed him among the group of those liable for death. (See Parashat Emor; Mishneh Torah, Admission into the Sanctuary 4.)

That a priest with a blemish not serve in the Temple: That a priest with a blemish not serve in the Temple service, as it is stated (Leviticus 21:17), "A man from your seed in their generations who has a blemish shall not approach to offer the bread of his God." [This is] meaning that he may not approach for the service, because all types of food are called bread in many places (see Rashi on Genesis 31:54). And this blemish [referred to in this context] is permanent. As so did they explain in Sifra, Emor, Section 3:5, "'Who has a blemish shall not approach' - I only have a permanent blemish. From where [do we know] a transient blemish? [Hence] we learn to say in the same section (Leviticus 21:18), 'any man who has a blemish shall not come close'" (meaning it is from another verse and not this one). And a permanent blemish is like a boil-scar or a protrusion, and that is a growth.