There are many causes for<unk>  including: Pre-testicular causes Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including: *Hypogonadism due to various causes *Drugs, alcohol, smoking *Strenuous riding (bicycle riding, horseback riding) *Medications, including androgens. Testicular factors Testicular factors refer to conditions where the testes produces semen of poor quality despite adequate hormonal support and include: *Age *Genetic defects on the Y chromosome * Y chromosome microdeletions *Abnormal set of chromosomes * Klinefelter syndrome *Neoplasm, e.g. seminoma *Cryptorchidism *Varicocele (14% in one study) *Trauma *Hydrocele *Mumps *Malaria *Defects in USP26 enzyme in some cases Mast cells releasing inflammatory mediators appear to directly suppress sperm motility in a potentially reversible manner, and may be a common pathophysiological mechanism for several of the above-mentioned factors. Post-testicular causes Post-testicular factors decrease male fertility due to conditions that affect the male genital system after testicular sperm production and include defects of the genital tract as well as problems in ejaculation: *Vas deferens obstruction *Lack of Vas deferens, often related to genetic markers for cystic fibrosis *Infection, e.g. prostatitis *Ejaculatory duct obstruction Idiopathic<unk>  (oligoasthenoteratozoospermia) In about 30% of infertile men no causative factor is found for their decrease in sperm concentration or quality by common clinical, instrumental, or laboratory means, and the condition is termed "idiopathic" (unexplained). A number of factors may be involved in the genesis of this condition, including age, infectious agents ( such as Chlamydia trachomatis), Y chromosome microdeletions, mitochondrial changes, environmental pollutants, and "subtle" hormonal changes. A review in 2013 came to the result that<unk>  and azoospermia are significantly associated with being overweight (odds ratio 1.1), obese (odds ratio 1.3) and morbidly obese (odds ratio 2.0), but the cause of this is unknown. It found no significant relation between<unk>  and being underweight. DNA damage The human breast cancer susceptibility gene 2 (BRCA2) is employed in homologous recombinational repair of DNA damages during meiosis. A common single-nucleotide polymorphism of BRCA2 is associated with severe<unk> . Men with mild<unk>  (semen concentration of 15 million to 20 million sperm/ml) were studied for an association of sperm DNA damage with life style factors. A significant association was found between sperm DNA damage and factors such as age, obesity and occupational stress.
Oligospermia
Hypospermia
Azoospermia
Hematospermia
Teratospermia
Asthenozoospermia
Globozoospermia
Dyschronometria