Causes of male infertility and poor sperm production include exposure to excessive heat from tight underwear, working long hours in hot places, smoking, alcohol and drug abuse, diseases such as diabetes and mumps, injury to the testes, or STIs like gonorrhea and chlamydia. Signs of infertility include poor quality of semen(low number of sperm or sperm that can't move), small amounts of semen(the normal amount in each ejaculation is about one spoonful), or semen that is too thick or watery.
Attribution: Straight Talk Foundation