Testicular problems--

   * undescended testicles
     * surgery of genital organs
       * trauma
        *cancer
        *congenital defects.
        *Blockage of testicular ducts sperm do not make it into the ejaculate.

  Hormonal problems--
         
*Low testosterone level
  * Prolonged use of medications
    *congenital disorders
     *tumours

  Ejaculation problems--

    *premature ejaculation (when ejaculation occurs too quickly)
     *retrograde ejaculation (when semen is ejaculated into the bladder).

  Lifestyle   Obesity--
        
Addictions
(Alcohol, Cigarette and Drugs)
         

Unhealthy food habits etc