What do Mormons believe about illness and causes of illness?
Simply put, Mormons seek to know, understand and believe anything that is true. We are encouraged to seek truth from all good sources. By-and-large, the origin of disease is not something specifically addressed by doctrine revealed through the priesthood. That leaves it up to individual members to decide what they believe personally, with the injunction to “seek ye diligently and teach one another words of wisdom; yea, seek ye out of the best books words of wisdom; seek learning, even by study and also by faith.” (D&C 88:118)
Mormons tend to accept well-established scientific truths, including truths about pathogens, genetics, nutrient deficiencies and other well-established causes of disease. Throughout recorded history, a common belief has been that disease is a punishment for sin. This idea isn’t entirely refuted by revealed doctrine, but it isn’t completely accepted either. Because many of the natural consequences of sin lead to poor health or disease, it can be said that disease is a punishment for certain sins. For example, illegitimate sex is against the the teachings of Jesus Christ and His servants. Such behavior can lead to sexually transmitted diseases that one would avoid by righteous living. In this sense you can say somebody is “punished” for illicit sexual behavior when they contract genital herpes. However, most Mormons would simply say that the disease was a natural consequence of sin, and not that the sin “caused” the disease.