text: from http://www.babyhopes.com/articles/causes-low-sperm-count.html\n\nCauses for LOW sperm count:\n\nTesticular Exposure to Overheating. \nOverheating (such as from high fever, saunas, and hot tubs) may temporarily lower sperm count. Work exposure to overheating may even impair fertility. \n\nSubstance Abuse\nCocaine or heavy marijuana use appears to temporarily reduce the number and quality of sperm by as much as 50%. Sperm actually have receptors for certain compounds in marijuana that resemble natural substances and which may impair the sperm's ability to swim and may also inhibit their ability to penetrate the egg. \n\nSmoking. \nSmoking impairs sperm count, sperm motility, reduces sperm lifespan, and may cause genetic changes that affect the offspring. Additionally, a 1999 study found that men who smoke have lower sex drives and less frequent sex. \n\nMalnutrition and Nutrient Deficiencies. \nDeficiencies in certain nutrients, such as vitamin C, selenium, zinc, and folate, may be particular risk factors for low sperm count in such cases. \n\nObesity. \nSome studies, but not all, have found an association between obesity in men and low sperm count.\n\nBicycling. \nBicycling has been linked to impotence in men and also may affect the sperm count. Pressure from the bike seat may damage blood vessels and nerves that are responsible for erections. Mountain biking, which involves riding on off-road terrain, exposes the perineum (the region between the scrotum and the anus) to more extreme shocks and vibrations and increases the risk for injuries to the scrotum. \n\nGenetic Factors \nGenetic factors are proving to be important contributors to male infertility. Such genetic conditions may be inherited or caused by environmental assaults. Inherited disorders can genetically impair fertility.\n\nEnvironmental Assaults \nOver exposure to environmental assaults (toxins, chemicals, infections) can reduce sperm count either by direct effects on testicular function or on the hormone systems, although the extent of the effect and specific environmental assaults involved are often controversial. Some chemicals that affect sperm production men are : Oxygen-Free Radicals, Estrogen emulation pesticidal chemicals (DDT, aldrin, dieldrin, PCPs, dioxins, and furans ), plastic softening chemicals like Phthalates, hydrocarbons (ethylbenzene, benzene, toluene, and xylene)\n\nExposure to Heavy Metals. \nChronic exposure to heavy metals such as lead, cadmium, or arsenic may affect sperm production and most often cause a reduced production in otherwise healthy males. Trace amounts of these metals in semen seem to inhibit the function of enzymes contained in the acrosome, the membrane that covers the head of the sperm. \n\nRadiation Treatment. \nRadiation treatments and x-rays affect any rapidly dividing cell, so cells that produce sperm are quite sensitive to radiation damage. Cells exposed to significant levels of radiation may take up to two years to resume normal sperm production, and, in severe circumstances, may never recover. \n\nLow Semen Levels \nA reduced amount of ejaculated semen (less than 0.5 milliliters per sample) may be caused by a structural abnormality in the tubes transporting the sperm. \n\nVaricocele\nA varicocele is a varicose vein in the cord that connects to the testicle. (A varicose vein is one that is abnormally enlarged and twisted.) Varicoceles are found in 15% to 20% of all men and in 25% to 40% of infertile men. It is not clear how they affect fertility, or even if they do at all.