- Age
- Genetic defects on the Y chromosome
- Abnormal set of chromosomes
- Neoplasm, e.g. seminoma
- Idiopathic failure
- Cryptorchidism
- Varicocele
- Trauma
- Hydrocele
- Mumps
- Malaria
- Testicular cancer
- Acrosomal defects affecting egg penetration
- Unexplained sperm deficiencies account for 30% of male infertility.
- Radiation therapy to a testis decreases its function, but infertility can efficiently be avoided by avoiding radiation to both testes.
- Vas deferens obstruction
- Lack of Vas deferens, often related to a disease (Cystic Fibrosis)
- Infection, e.g. prostatitis
- Retrograde ejaculation
- Ejaculatory duct obstruction
- Impotence