Positive symptoms, such as delusions and hallucinations (especially of voices), are common, and any Schneiderian first-rank symptoms are particularly indicative of the illness. Negative symptoms include social withdrawal, impairment of ego boundaries, and loss of energy and initiative. Schizophrenia is diagnosed only if symptoms persist for at least one month. The illness can spontaneously remit, run a course with infrequent or frequent relapses, or become chronic. The prognosis has improved with antipsychotic drugs and with vigorous psychological and social management and rehabilitation. The many causes include genetic factors, environmental stress, and various triggering factors.