The production of sperm is a complex process and requires normal functioning of the testicles (testes) as well as the hypothalamus and pituitary glands — organs in your brain that produce hormones that trigger sperm production. Once sperm are produced in the testicles, delicate tubes transport them until they mix with semen and are ejaculated out of the penis. Problems with any of these systems can affect sperm production.
Also, there can be problems of abnormal sperm shape (morphology), movement (motility) or function.
However, often the cause of low sperm count isn't identified.
Low sperm count can be caused by a number of health issues and medical treatments. Some of these include:
- Varicocele. A varicocele (VAR-ih-koe-seel) is a swelling of the veins that drain the testicle. It's the most common reversible cause of male infertility. Although the exact reason that varicoceles cause infertility is unknown, it might be related to abnormal testicular temperature regulation. Varicoceles result in reduced quality of the sperm.
- Infection. Some infections can interfere with sperm production or sperm health or can cause scarring that blocks the passage of sperm. These include inflammation of the epididymis (epididymitis) or testicles (orchitis) and some sexually transmitted infections, including gonorrhea or HIV. Although some infections can result in permanent testicular damage, most often sperm can still be retrieved.
Ejaculation problems. Retrograde ejaculation occurs when semen enters the bladder during orgasm instead of emerging out of the tip of the penis. Various health conditions can cause retrograde or lack of ejaculation, including diabetes, spinal injuries, and surgery of the bladder, prostate or urethra.
Certain medications also might result in ejaculatory problems, such as blood pressure medications known as alpha blockers. Some ejaculatory problems can be reversed, while others are permanent. In most cases of permanent ejaculation problems, sperm can still be retrieved directly from the testicles.
- Antibodies that attack sperm. Anti-sperm antibodies are immune system cells that mistakenly identify sperm as harmful invaders and attempt to destroy them.
- Tumors. Cancers and nonmalignant tumors can affect the male reproductive organs directly, through the glands that release hormones related to reproduction, such as the pituitary gland, or through unknown causes. Surgery, radiation or chemotherapy to treat tumors can also affect male fertility.
- Undescended testicles. During fetal development one or both testicles sometimes fail to descend from the abdomen into the sac that normally contains the testicles (scrotum). Decreased fertility is more likely in men with this condition.
- Hormone imbalances. The hypothalamus, pituitary and testicles produce hormones that are necessary to create sperm. Alterations in these hormones, as well as from other systems such as the thyroid and adrenal gland, may impair sperm production.
Defects of tubules that transport sperm. Many different tubes carry sperm. They can be blocked due to various causes, including inadvertent injury from surgery, prior infections, trauma or abnormal development, such as with cystic fibrosis or similar inherited conditions.
Blockage can occur at any level, including within the testicle, in the tubes that drain the testicle, in the epididymis, in the vas deferens, near the ejaculatory ducts or in the urethra.
- Chromosome defects. Inherited disorders such as Klinefelter's syndrome — in which a male is born with two X chromosomes and one Y chromosome instead of one X and one Y — cause abnormal development of the male reproductive organs. Other genetic syndromes associated with infertility include cystic fibrosis, Kallmann's syndrome and Kartagener's syndrome.
- Celiac disease. A digestive disorder caused by sensitivity to gluten, celiac disease can cause male infertility. Fertility may improve after adopting a gluten-free diet.
- Certain medications. Testosterone replacement therapy, long-term anabolic steroid use, cancer medications (chemotherapy), certain antifungal and antibiotic medications, some ulcer medications and other medications can impair sperm production and decrease male fertility.
- Prior surgeries. Certain surgeries might prevent you from having sperm in your ejaculate, including vasectomy, inguinal hernia repairs, scrotal or testicular surgeries, prostate surgeries, and large abdominal surgeries performed for testicular and rectal cancers, among others. In most cases, surgery can be performed to either reverse these blockages or to retrieve sperm directly from the epididymis and testicles.
Sperm production or function can be affected by overexposure to certain environmental elements, including:
- Industrial chemicals. Extended exposure to benzenes, toluene, xylene, herbicides, pesticides, organic solvents, painting materials and lead might contribute to low sperm counts.
- Heavy metal exposure. Exposure to lead or other heavy metals also can cause infertility.
- Radiation or X-rays. Exposure to radiation can reduce sperm production. It can take several years for sperm production to return to normal. With high doses of radiation, sperm production can be permanently reduced.
Overheating the testicles. Elevated temperatures impair sperm production and function. Although studies are limited and are inconclusive, frequent use of saunas or hot tubs might temporarily impair sperm count.
Sitting for long periods, wearing tight clothing or working on a laptop computer for long stretches of time also might increase the temperature in your scrotum and slightly reduce sperm production.
Health, lifestyle and other causes
Other causes of low sperm count include:
- Drug use. Anabolic steroids taken to stimulate muscle strength and growth can cause the testicles to shrink and sperm production to decrease. Use of cocaine or marijuana might reduce the number and quality of your sperm as well.
- Alcohol use. Drinking alcohol can lower testosterone levels and cause decreased sperm production.
- Occupation. Certain occupations might be linked with a risk of infertility, including welding or those associated with prolonged sitting, such as truck driving. However, the data to support these associations is inconsistent.
- Tobacco smoking. Men who smoke might have a lower sperm count than do those who don't smoke.
- Emotional stress. Severe or prolonged emotional stress, including stress about fertility, might interfere with hormones needed to produce sperm.
- Weight. Obesity can impair fertility in several ways, including directly impacting sperm and by causing hormone changes that reduce male fertility.
- Sperm testing issues. Lower than normal sperm counts can result from testing a sperm sample that was taken too soon after your last ejaculation; was taken too soon after an illness or stressful event; or didn't contain all of the semen you ejaculated because some was spilled during collection. For this reason, results are generally based on several samples taken over a period of time.