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".

Symptoms of genophobia can be feeling of panic, terror, and dread. Other symptoms are increased speed of heartbeat, shortness of breath, trembling/shaking, anxiety, sweating, crying, and avoidance of others.

Some sufferers of genophobia may develop the fear as a result of preexisting fears. Some people may have nosophobia: the fear of contracting a disease or virus. They may also have gymnophobia: the fear of nudity. Others may have extreme fear of being touched. These issues, along with stress disorders, can manifest themselves as the innate fear of sex.

Most patients report acute anxiety attacks due to perceived genital retraction and/or genital shrinkage, despite a lack of any objectively visible biological changes in the genitalia that are longstanding. "Longstanding" refers to changes that are sustained over a significant period and do not appear reversible, unlike the effect of cold temperatures on some genital regions that cause retraction. These changes may trigger a koro attack when observed, although the effects of cold temperatures are objectively reversible. According to literature, episodes usually last several hours, though the duration may be as long as two days. There are cases in which koro symptoms persist for years in a chronic state, indicating a potential co-morbidity with body dysmorphic disorder. In addition to retraction, other symptoms include a perception of alteration of penis shape and loss of penile muscle tone. In cases when sufferers have no perception of retraction, some patients may complain of genital paraesthesia or genital shortening. Among females, the cardinal symptom is nipple retraction in the breast, generally into the breast as a whole.

Psychological components of koro anxiety include fear of impending death, penile dissolution and loss of sexual power. Feelings of impending death along with retraction and perceived spermatorrhea has a strong cultural link with Chinese traditional beliefs. This is demonstrated by the fact that Asians generally believe koro symptoms are fatal, unlike most patients in the West. Other ideational themes are intra-abdominal organ shrinkage, sex change to female or eunuch, non-specific physical danger, urinary obstruction, sterility, impending madness, spirit possession and a feeling of being bewitched.

Extremely anxious sufferers and their family members may resort to physical methods to prevent the believed retraction of the penis. A man may perform manual or mechanical penile traction, or "anchoring" by a loop of string or some clamping device. Similarly, a woman may be seen grabbing her own breast, pulling her nipple, or even having iron pins inserted into the nipple. Physical injury may occur from these attempts. These forceful attempts often lead to injuries, even death.

Men who present with this complaint may have Koro, but they may also be misinformed about normal genital size. Additionally, they may be suffering from penile dysmorphophobia. Penile dysmorphophobia is related to body dysmorphic disorder (BDD), defined by the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (Text Revision) (DSM-IV-TR) as a condition marked by excessive preoccupation with an imaginary or minor defect in a facial feature or localized part of the body. BDD is different from Koro. In Koro, a patient is overcome with the belief that his penis is actively shrinking, and it may be in imminent danger of disappearing. Clinical literature indicates that these two psychological conditions should be separated during differential diagnosis.

In addition to differentiating Koro from body dysmorphic disorder, physicians also recommend that differential diagnosis separates Koro from physical urological abnormalities. For example, one physical disorder that causes loss of penile size is Peyronie's disease, where the tunica albuginea develops scar tissue that prevents the full expansion of an erection and causes flaccid penis retraction. Additionally, a buried penis is a normally developed penis, partially covered by the suprapubic fat which can be surgically removed.