Proposed explanations include lifestyle factors, such as changes in diet and physical activity levels, and increased exposure to endocrine disrupting chemicals, such as those found in plastics and pesticides.
[12] Academia and the scientific community have reached consensus in favor of the use of the term male infertility crisis, citing it as necessary to prompt preventative action to remedy the issue in the present time before it affects future generations on a greater scale.
[12] Media coverage increased during the 2010s, often coinciding with (or in response to) releases of studies and using words like "crisis", "apocalypse", "time bomb", and "threat to the human race".
[11] Other reports published during the two decades had not found similar declines; a 1982 research paper by Niecheslag et al. concluded that there were no changes in semen quality.
[18] The decline in sperm quality reflected a shift in societal patterns of sexual behaviour, widespread recreational drug use, and preferences for marriage and fatherhood later in life.
[19] The World Health Organization published its first laboratory manual for semen analysis in 1980, which sets global standard parameters for the measurement of sperm quality and normality.
A 1992 Danish meta-analysis, commonly known as the Carlsen study after its principal author, showed that between 1938 and 1990 a population described as healthy had experienced a significant decrease in sperm count and semen volume.
[25] Two other studies presented at the 2018 American Society for Reproductive Medicine (ASRM) scientific congress had similar findings: reduced sperm counts and motility during the 2000s.
[35] Other national-government responses include recommendations by the UK's National Health Service for a healthy lifestyle and loose-fitting underwear to improve fertility.
[12] Scientists disagree on the impact of observed fertility declines to date, and sperm counts remain above the 15 million considered to be below normal by the World Health Organization.
[39] It has also been pointed out that sexual and masturbatory cultural shifts may be the true driver of the phenomenon, as more frequent ejaculation quickly reduces sperm counts.