The status of a Kohen who is a Challal [born from forbidden relations]:
A Challal is a Kohen who is desecrated from his priesthood position, and is hence not considered like a non-Kohen regarding all matters, as we will explain below.
A. Who is defined as a Challal?
Biblical-Issureiy Kehuna: Any child who was born from parents who were in a Biblically Kehuna prohibited relationship, whether within wedlock or out of wedlock, is defined as a Challal. Meaning, that if a man who is a Kohen has a child with a woman to whom he is Biblically prohibited in marrying due to his status of priesthood, then any offspring born from that union is defined as a Challal. For example, if a Kohen had a child with a divorcee, or a woman who is Halachically defined as a Zoneh, or a woman who herself was already defined as a Challalah, then that child is considered a Challal.
Rabbinical Issureiy Kehuna: A child who was born from parents who were in a Rabbinically Kehuna prohibited relationship is defined as a Rabbinical Challal. For example, if a Kohen had a child with a Chalutza, then that child is considered a Challal.
B. His status:
A person who is defined as a Challal is considered like a non-Kohen regarding all matters, including:
- Nesias Kapayim: A Challal cannot go up to the Duchan to recite Nesias Kapayim, and in this regard he is considered like a non-Kohen to whom there is a prohibition against them performing Nesias Kapayim, and if he does so then he transgresses a positive command just as a Non-Kohen with transgress. Even a Rabbinical Challal does not perform Nesias Kapayim.
- Aliyah to Torah as Kohen: A Kohen who is a Challal may not be given the first Aliyah.
- Defiling himself to the dead: A Kohen who is a [Biblical] Chalal is not prohibited from defiling himself to the dead [i.e. Tumas Meis]. However, a Rabbinical Chalal is Biblically prohibited from defiling himself to the dead Tumas Meis.
- Pidyon Haben: A Kohen who is a Challal is obligated to redeem his son who is a firstborn to the mother, and to give the money to a Kohen. If the father is a Kohen although his child is a Chalal [i.e. a Kohen married a woman who is forbidden to Kehuna, such as a divorcee, and she birthed him a firstborn son] then the child needs to be redeemed. Nevertheless, the Kohen father can keep the money for himself after he separates it for the Pidyon.
- Marrying a divorcee or other women prohibited to the Kehuna: A Kohen who is a Biblical Challal is permitted to marry a divorcee or any other woman prohibited to the priesthood. However, a Rabbinical Challal remains Biblically prohibited from marrying a woman who is prohibited to the priesthood.
- Serving in the Temple: A Challal is prohibited from serving in the Temple, just like a non-Kohen.
- Eating Teruma and Kodshim: A Challal is prohibited from eating Teruma and Kodshim, just like a non-Kohen.
 See Admur 128:55; Michaber E.H. 7:20; Encyclopedia Talmudit Erech Challal
 See Admur ibid; Michaber E.H. 7:12-19
 See Michaber E.H. 6:1 and 7:12
 A woman is defined as a Zonah if she had relations with a gentile, or an Erva [i.e. brother, father, etc], or a Challal [Michaber E.H. 6:8] or committed adultery or was raped while marriage [Michaber E.H. 6:10-11], or had relations with a Mamzer.
A gentile: A gentile is considered a Zonah. [Michaber E.H. 7:14]]
A convert: A woman who was born a gentile and converted is considered a Zonah, even if she converted before age 3. [Michaber E.H. 7:14]
 A Challalah is defined as 1) Any woman who was born from a Biblically Kehuna prohibited relationship. b) Any woman who is prohibited to the priesthood, who married or had relations with a Kohen [i.e. divorcee, Zonah]. [Michaber E.H. 7:12]
 Admur ibid
 Admur ibid; Michaber E.H. 7:20
 Admur ibid; Michaber E.H. 7:20; Levush 128
 Admur 128:55
 Admur ibid; Michaber 128:42; Rambam Tefila 15:5
 Admur ibid in parentheses; Peri Chadash 128
 Admur ibid; M”A 128:63; Elya Raba 128:78
The reason: Although the performance of the priestly blessing is a Biblical command in the Torah and a Kohen who does not do so after being requested transgresses this positive command, nonetheless, the sages have permission to uproot a biblical matter in a passive way. [Admur ibid]
 Michaber Y.D. 373:2; E.H. 7:20
 Shach 373:2 in name of Bach; See also Michaber E.H. 7:20
 See Michaber E.H. 7:12 that a Chalal has the status of a Zar
 Michaber Y.D. 305:19; Levush 305:19; Maharit Algazi Hilchos Bechoros on Ramban 67 in name of Rosh; Aruch Hashulchan 305:60; Pidyon Haben Kehilchaso 3:14; Shevach Habris 1:5
 Michaber E.H. 7:20
 Zevachim 13a; Encyclopedia Talmudit Erech Challal 3
 Encyclopedia Talmudit Erech Challal 4