The exact cause of premature ejaculation isn't known. While it was once thought to be only psychological,  premature ejaculation is more complicated and involves a complex interaction of psychological and biological factors. A number of biological factors may contribute to premature ejaculation, including: Abnormal hormone levelsAbnormal levels of brain chemicals called neurotransmittersAbnormal reflex activity of the ejaculatory systemCertain thyroid problemsInflammation and infection of the prostate or urethraInherited traitsNerve damage from surgery or trauma (rare) psychological causes Situations in which you may have hurried to reach climax in order to avoid being discoveredGuilty feelings that increase your tendency to rush through sexual encounters