Has Islamic law forbidden marriage between relatives due to the hereditary diseases it causes?
The Islamic Sharia has prohibited marriage to some relatives, such as mothers, daughters, paternal aunts, and maternal aunts, while permitting marriage to others, such as paternal cousins (daughter of a paternal uncle) and maternal cousins (daughter of a maternal uncle). What is raised about the harms of consanguineous marriage from a medical perspective requires proof, as the incidence of hereditary diseases resulting from it is very small. Some doctors even believe that consanguineous marriage has health benefits. It has not been authentically reported from the Prophet, peace and blessings be upon him, anything that prohibits consanguineous marriage. Rather, he himself married his paternal aunt's daughter and married his daughter to his paternal cousin. The early Muslims (Salaf) also married their relatives. Therefore, the choice depends on the characteristics of the man and the woman, and there should be no fear of having deformed offspring.
Summarized from the full answer at Ftawy · reviewed Sep 2, 2026
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