Spermatogenesis and ovulation in males and females, respectively, may be impaired by hypogonadism, which, depending on the degree of severity, may result in partial or complete infertility.
A man with low levels of testosterone may lose his desire for sex. Sexual stimulation and sexual activity cause testosterone levels to rise. Testosterone levels can drop during a long period of sexual inactivity.
Hypogonadism can involve just hormone production or just fertility, but most commonly involves both. Examples of hypogonadism that affect fertility more than hormone production are Klinefelter syndrome and Kartagener syndrome (a rare hereditary disease that causes defects in the action of cilia lining the respiratory tract and fallopian tube, as well as in the flagella of sperm cells).