According to Dr. Miles Groth, head of the Psychology Department at Wagner College, jealousy starts at infancy. A baby feels envy when she feels that her close bond with her mother is encroached upon, first by her father and then by a new sibling. Clinical sexologist Brigitte Paquette adds that if a young child is not shown an appropriate level of affection, this could lead to low self-esteem, making the child more likely to be jealous later in life.

Paquette says jealousy is a natural emotion, and Groth goes so far as to say it is essential. When a baby first feels envious, it allows him to become less dependent on his mother and form relationships with other people, Groth says. According to Paquette, it is perfectly reasonable for someone to feel envy. “[It] is usually normal to feel jealous when we risk losing a person that we are deeply attached to,” she says. Dr. Vijai P. Sharma adds that those who feel a healthy level of jealousy become less envious as they become more serious with their partner.

Groth's colleague at Wagner College, Connie Salhany, says jealousy can be comprised of fear, rage, anger and sadness. It is when these emotions reach uncontrollable levels that jealousy becomes unhealthy. Salhany adds that this can be marked by paranoia and delusions and could lead to abusive behavior such as stalking. This psychological condition is called conjugal paranoia, or morbid jealousy. Extreme jealousy and paranoia usually stem from tremendous insecurity, says Paquette. The jealous individual fears being cheated on or abandoned. The paranoia become so overwhelming that she actually believes that her partner has been unfaithful, even if these delusions are unwarranted. Partners of jealous individuals may feel like they cannot answer the phone, talk to others or even leave the house, because they cannot deal with their significant other’s paranoia.

Judith A. Easton and her colleagues at the University of Texas conducted a study of morbidly jealous individuals. They found that men tend to be jealous of other men that are upper class and financially well off and are paranoid about their female partners sexually cheating on them. Women tend to be insecure about young and attractive women and worry that their male partners will emotionally bond with them.

Sharma, Groth, Paquette and Salhany all agree that those who are morbidly jealous can be treated with therapy. According to Sharma, individual therapy is most effective. The goal of therapy is for the conjugally paranoid individual to identify the source of his discomfort realize where his jealousy stems from and to become more confident in his self. Paquette adds that a partner cannot force his significant other to seek therapy. She first has to admit she has a problem.