Nosophobia is the irrational fear of contracting a disease, a type of specific phobia. Primary fears of this kind are fear of contracting HIV, pulmonary tuberculosis, venereal diseases, cancer, and heart diseases.

Some authors have suggested that the medical students' disease should accurately be referred to as "nosophobia" rather than "hypochondriasis", because the quoted studies show a very low percentage of hypochondriacal character of the condition.

The word "nosophobia" comes from the Greek νόσος "nosos" for "disease".

There can be many different reasons for why people develop genophobia. Some of the main causes are former incidents of sexual assaults or abuse. These incidents violate the victim’s trust and take away their sense of right to self-determination. Another possible cause of genophobia is the feeling of intense shame or medical reasons. Others may have the fear without any diagnosable reason.

Some people may become afflicted with genophobia because of body image issues. Some men and women can become obsessively self-conscious of their bodies. This may be regarding their entire physique or it may be focused on one specific issue. Women may become insecure if they dislike the appearance of their labia majora or labia minora. Men may become genophobic if they suffer from erectile dysfunction. Others who grapple with gender dysphoria can also develop a fear of sex.

Psychosexual conflicts, personality factors, and cultural beliefs are considered as being of etiological

significance to koro. Sexual adjustment histories of non-Chinese victims are often significant, such as premorbid sex inadequacy, sexual promiscuity, guilt over masturbation, and impotence.

When considering the biological mechanisms and evolutionary history of koro, it is important to look at it in the larger framework of mass hysteria. While the underlying mechanisms are still poorly understood, it has been suggested that the mirror neurons play a major role in mass hysteria outbreaks. Mirror neurons, which have been found in both human and non-human primates, are neurons that fire when one performs an action and when they observe another individual performing the same action. It is hypothesized that we evolved these mechanisms to learn from observation of others, as well as to facilitate imitation. However, within mirror neurons, there is some form of inhibitory process, which prevents us from blindly mimicking every action we observe others perform. New research into this area suggests that in mass hysteria outbreaks something goes amiss in this inhibitory process.