Sexual difficulties may begin early in a person's life, or they may develop after an individual has previously experienced enjoyable and satisfying sex. A problem may develop gradually over time, or may occur suddenly as a total or partial inability to participate in one or more stages of the sexual act. The causes of sexual difficulties can be physical, psychological, or both.

Emotional factors affecting sex include both interpersonal problems and psychological problems within the individual. Interpersonal problems include marital or relationship problems, or lack of trust and open communication between partners. Personal psychological problems include depression, sexual fears or guilt, or past sexual trauma.

Physical factors contributing to sexual problems include:

• Injuries to the back
• An enlarged prostate gland
• Disease (diabetic neuropathy, multiple sclerosis, tumours, and, rarely, tertiary syphilis)
• Drugs, such as alcohol, nicotine, narcotics, stimulants, antihypertensives (medicines that lower blood pressure), antihistamines, and some psychotherapeutic drugs (used to treat psychological problems such as depression)
• Endocrine disorders (thyroid, pituitary, or adrenal gland problems)
• Failure of various organs (such as the heart and lungs)
• Hormonal deficiencies (low testosterone, oestrogen, or androgens)
• Nerve damage (as in spinal cord injuries)
• Problems with blood supply
• Some birth defects