Persistent delusional disorder is a psychotic disorder characterized by the presence of one or more persistent delusions that last for at least one month. A delusion is a fixed false belief that is firmly held despite clear evidence to the contrary and cannot be explained by the person's cultural or religious background. Unlike schizophrenia, individuals with persistent delusional disorder usually do not have marked disturbances in thought, perception, or personality, and their daily functioning often remains relatively preserved except in areas directly influenced by the delusion. The disorder generally develops during middle or late adulthood, although it can occur at any age. The onset is usually gradual, and the beliefs become stronger over time. People affected often appear normal in conversation until the topic of their delusion is discussed. They may defend their beliefs with strong conviction and reject any logical explanation or contradictory evidence. The exact cause