Published online by Cambridge University Press: 13 June 2014
Jealousy is a commonly experienced emotion which has been observed in infants as young as 5-6 months of age and across the lifespan of an individual. In its extreme form jealousy can be pathological, when the belief which may be a delusion, obsession or an overvalued idea, is held on inadequate grounds and is unaffected by rational discussion.
Morbid jealousy differs from normal jealousy in its intensity or rationality. It can be thought of as hypersensitive jealousy since jealous reactions are experienced at a much lower threshold than in average individuals. Morbid jealousy is a disorder in which an individual believes that their partner is, or will be, sexually unfaithful.
Morbid jealousy can occur when a partner is in fact being unfaithful, provided that the evidence for the infidelity is incorrect and there is an excessive or irrational response to such evidence. The preoccupation with the partner's infidelity is often triggered by vivid mental images of their partner's past or present relationships.