stress, acute febrile illnesses, and other illnesses and drugs may suppress gonadotrophin release resulting in decreased sperm production of the subsequent 1-3 months
very high levels of exercise
seminal cytokines and reactive oxygen species increased during aerobic and non-aerobic isometric exercise
in professional athletes like soccer and rugby players, neutrophils and superoxide dismutase (SOD) levels were elevated after a match and the season.
semen impairment is observed in mountaineers with higher altitudes (> 2000 m), along with the risk of hypoxia
excessive scrotal temperatures:
40% decline in sperm concentration for every 1 °C rise in scrotal temperature
heat exposure such as saunas or spas may reduce sperm production in short term
sedentary work conditions elevate scrotal temperature by an average of 0.7 °C and up to 2.2 °C in car drivers 3)
infertility rate in Saudi Arabian bakers exposed to a wet-bulb globe temperature (WBGT) of 37 °C was 22.7% compared to 3% in healthy volunteers
in steel industry workers exposed to a WBGT of 36 °C, sperm parameters such as morphology, count, motility, and semen volume significantly differed from those unexposed
< 30% sperm with normal morphology (teratospermia):
excessive exposure to heat or radiation
infectious processes
oligospermia (< 20 million sperm per mL):
azoospermia
more likely to have a chromosomal abnormality (10-15%) than infertile men with sperm density within the reference range (1%)
ejaculatory duct obstruction
hypogonadotropism
Young's syndrome - obstructive azospermia with chronic suppurative lung conditions
cystic fibrosis - absence of vas deferens
NB. a study published Jan 2024 suggests semen microbiome can also adversely affect male fertility - particularly Lactobacillus iners and Pseudomonas stutzeri5)