There is no definition of incest in India’s penal code.
As a result, persons who engage in incest cannot be prosecuted for the crime of incest, but they can be prosecuted for any other legal reason, such as adultery, sodomy, or rape.
Personal laws of Hindus and Muslims provisions prohibit incest.
Marriage between banned degrees of kinship and sapindas is forbidden in Hinduism.
According to the Hindu Marriage Act, two people cannot marry if they are within a prohibited degree of relationship.
Section 5 of the Hindu Marriage Act prohibits marriage between a brother and sister, uncle and niece, aunt and nephew, or children of a brother and sister or of two brothers or sisters, among other things unless the community’s tradition allows it, the marriage is null and invalid.
In Muslims, it is forbidden for men to marry their sisters, foster sisters, step sisters, mother’s, mother’s sister’s, father’s sister’s, brother’s daughter, sister’s daughter, step-daughters, and this is considered incest.
First cousin marriage is allowed in Muslims it is not incest under muslim personal laws.
Close blood connections, like personal laws, are banned degrees of kinship under the special marriage statute.
Relationships in which two persons are derived from the same ancestor but married to separate women or when they are descended from the same ancestress.
Reference: Section 5 in The Hindu Marriage Act, 1955
Conditions for a Hindu marriage.
A marriage may be solemnized between any two Hindus, if the following conditions are fulfilled, namely:
(iv) the parties are not within the degrees of prohibited relationship unless the custom or usage governing each of them permits of a marriage between the two;
(v) the parties are not sapindas of each other, unless the custom or usage governing each of them permits of a marriage between the two….
Schedule 1 part 2 of the special marriage act covers the laws related to prohibition of marriage.