Malaikah (Angels) & Jinns (Invisible Beings)
Their potential to cause diseases and psychological disorders
Islam does inform us about various abilities of the jinn shayateen (devils) including potential harms such as causing diseases. There is an authentic hadith of Prophet Muhammad ﷺ that is the key to understanding this topic: “The satan flows through the son of Adam like blood.” The Prophet ﷺ told us a very important fact about their ability to flow inside of us like blood flows inside our veins. Due to their fiery nature like radiation, there is likely chance that they can penetrate our biological as well as neurological systems. The term majnoon coming from the root jinn, refers to someone who is not in his senses as their intellect is covered. Thus, a person suffering from some sort of mental disorder is usually referred to as a majnoon in Arabic and other Eastern languages. The renown Turkish Islamic scholar named Fethullah Gulen said something very important in reference to the prophetic warning and gave a an advice to those in the medical profession: “Jinn can penetrate a body even deeper than X-rays. They can reach into a being's veins and the central points of the brain. They seem to be like lasers, which are used in everything from computers to nuclear weaponry, from medicine to communication and police investigations, and to removing obstructions in our veins and arteries. So, when we consider that satan and all jinn are created from smokeless fire that penetrates deep into the body, like radiation or radioactive energy, we can understand the meaning of the Prophetic Tradition: ‘satan moves where the blood moves.’ Jinn can harm the body and cause physical and psychological illnesses. It might be a good idea for medical authorities to consider whether jinn cause certain types of cancer, since cancer is an unordered and diseased growth in the body that we can describe as cellular anarchy. Maybe some jinn have settled in that part of the body and are destroying its cellular structure.” Interestingly American Cancer Society claims that no one knows the exact cause of most cases of cancer. They know certain changes in our cells can cause cancer to start, but do not yet know exactly how it all happens. Scientists are still studying this problem.
As per Islamic texts the jinn are various types and not all are bad, there are many that are good and believers. The ones that harm us for no reason are always the devils or shayateen. As per prophetic traditions some are small and so their harm is relatively much lesser such as making us catch some sort of illness etc. So it could very well be that somebody suffering from a mental disorder like schizophrenia or disease like cancer, be affected by a devil. To repel their effects Muslims usually listen and recite a sort of an exorcism called ruqyah (healing) which includes certain verses from the Quran that have a therapeutic effect which gradually heals the patient. From personal experience, my mother got diagnosed with cancer and in addition to the medical therapy, continuously listening to ruqyah had a very miraculous healing affect that finally cured her. Interestingly in our modern times when cancer has become a global epidemic ruqyah has proven to be very effective for cancer patients, along with medicine, in the Islamic world. Most important method to protect yourself from their harms is that we Muslims are told to follow the lifestyle of the Prophet ﷺ as much as possible.
 Sunan Abi Dawud 4719
 Jinn and Human Beings - Gulen 2001
 American Cancer Society - team 2018