•   Psychological                       

1. stress and anxiety from work/home
2. performance anxiety
3. marital discord
4. unresolved sexual myths and beliefs
5. depression

•     Organic

1. Neurogenic

   Lesion in brain, spinal cord,ccavernour and pudendal nerves,and smooth muscle receptors caused by deficiency in the sensory, motor, autonomic neural pathway or in the neurotransmitter.

2. Vasculogenic

  Arteriogenic

•     Hyperlipidemia, hypertension
•     Pelvic/perineal trauma
•     Pelvic irradiation
•     Smoking
•     Diabetes

Venogenic

•      Fibrotic lesions
•      Degenerative changes
•      Veno-occlusive disorder

3. Endocrinological

•       Hypogonadism
•       Hyperpralactinemia
•       Hyper thyroidism
•       Diabetes

4. Drug induced

•      Anti psychotic and antidepressant drugs
•     Alcoholism
•     Cimetidine etc

5. Miscellaneous

•      Aging
•      Systemic diseases