Roughly one in six people of reproductive age worldwide experience infertility at some point in their lives, and the causes span a wide range: hormonal conditions, structural problems, infections, age, environmental exposures, and medical treatments. Some are reversible, others are permanent, and many go undetected until a person actively tries to conceive. Here’s what can actually interfere with fertility in both men and women.
Ovulation Disorders
For women, the single most common category of infertility involves problems with ovulation. If an egg isn’t released on a regular cycle, conception either can’t happen or becomes far less likely.
Polycystic ovary syndrome (PCOS) is the leading cause of female infertility. It creates a hormone imbalance that disrupts ovulation, and it’s closely linked with insulin resistance, weight gain, acne, and excess hair growth on the face or body. Many women with PCOS don’t realize they have it until they struggle to get pregnant.
Extreme stress, very high or very low body weight, and rapid weight changes can also shut down ovulation by disrupting the hormonal signals your brain sends to your ovaries each month. The pituitary gland produces two key hormones that trigger egg release, and when physical or emotional stress throws those signals off, ovulation can stop entirely. This is sometimes called hypothalamic dysfunction, and it’s often reversible once the underlying trigger is addressed.
Less commonly, the pituitary gland overproduces a hormone called prolactin, which suppresses estrogen and can halt ovulation. Certain medications can trigger this as a side effect.
Primary Ovarian Insufficiency
Some women lose ovarian function before age 40. The ovaries stop releasing eggs and produce less estrogen, effectively creating early menopause. This can result from autoimmune conditions, genetic factors, or damage from treatments like chemotherapy. Unlike PCOS or stress-related ovulation problems, primary ovarian insufficiency is often permanent and significantly harder to treat.
Structural Problems in the Reproductive Tract
Even when ovulation works normally, physical blockages or scarring can prevent sperm from reaching the egg or stop a fertilized egg from implanting in the uterus.
Blocked or damaged fallopian tubes are a major factor. The most common culprit is pelvic inflammatory disease (PID), an infection of the upper reproductive tract typically caused by sexually transmitted bacteria like chlamydia or gonorrhea. PID can destroy the delicate tissue lining the fallopian tubes. What makes it particularly dangerous is that even mild or symptom-free infections can cause enough scarring to block the tubes. Delayed treatment significantly raises the risk of permanent damage.
Endometriosis is another common structural cause. Tissue similar to the uterine lining grows in places it shouldn’t, often on the ovaries, fallopian tubes, or pelvic walls. This tissue causes chronic inflammation and scarring that can physically block the path between egg and sperm. Endometriosis also appears to reduce fertility in less obvious ways, possibly by damaging egg or sperm quality directly. Surgical removal of the tissue can help, but the surgery itself sometimes creates additional scarring.
Previous abdominal or pelvic surgeries, including surgery for ectopic pregnancy, can also leave scar tissue that interferes with fertility.
Male Factor Infertility
Male factors contribute to roughly half of all infertility cases, yet they’re often overlooked. The most common identifiable cause is a varicocele, an enlargement of veins inside the scrotum. Varicoceles are present in about 15% of all men, but they show up in 40% of men being evaluated for infertility. Among men who previously fathered children but are now struggling (secondary infertility), varicoceles account for up to 70% of cases.
The primary way a varicocele damages fertility appears to be through heat. Impaired blood circulation raises the temperature inside the testicles, and sperm production is highly sensitive to even small temperature increases. The result is lower sperm counts, reduced motility, and abnormal sperm shape.
Beyond varicoceles, male infertility can stem from hormonal imbalances, genetic conditions, undescended testicles, infections that damage reproductive tissue, and ejaculation disorders. Lifestyle factors like heavy alcohol use, smoking, anabolic steroid use, and exposure to industrial chemicals also impair sperm production.
Age
Age is one of the most significant and least modifiable fertility factors, particularly for women. A healthy, fertile 30-year-old woman has about a 20% chance of conceiving in any given month. By 40, that drops below 5% per cycle. By 43, even IVF success rates fall below 5%, and by 45, using donor eggs becomes the only realistic path to pregnancy for most women.
This decline happens because both the number and quality of eggs decrease over time. Women are born with all the eggs they’ll ever have, and as those eggs age, they’re more likely to carry chromosomal abnormalities that prevent successful implantation or lead to miscarriage.
Men also experience age-related fertility decline, though it’s more gradual. Sperm quality, including motility and DNA integrity, decreases with age, and older paternal age is associated with longer time to conception and higher miscarriage rates.
Environmental and Chemical Exposures
A growing body of evidence links certain chemicals to reproductive harm in both sexes. Endocrine-disrupting chemicals interfere with the hormones that regulate fertility. The most well-studied include BPA (found in some plastics and food container linings), phthalates (common in personal care products and soft plastics), and certain pesticides, including organochlorine and organophosphorus compounds.
These chemicals can interfere with egg development in women and reduce sperm quality in men. Some, like polychlorinated biphenyls, have been banned in many countries, but they persist in the environment and can still be detected in human tissue. Occupational exposure to industrial solvents, heavy metals, and high heat (for men) also poses fertility risks.
Cancer Treatment
Chemotherapy, radiation, and related cancer therapies are among the most potent threats to fertility. Certain chemotherapy drugs, particularly a class called alkylating agents, can destroy the immature eggs stored in the ovaries, leading to primary ovarian insufficiency. The risk increases with higher doses and combination drug regimens.
Radiation therapy directed at or near the pelvis can damage the ovaries, destroy eggs, or scar the uterus in ways that prevent implantation or increase pregnancy complications. Radiation to the brain can disrupt the hormonal signals that control ovulation. For men, pelvic or testicular radiation can severely reduce or eliminate sperm production.
Surgeries for cancers in the abdomen or pelvis sometimes require removing reproductive organs entirely. Even when organs are preserved, post-surgical scarring can block fallopian tubes or prevent eggs from reaching the uterus. Patients preparing for cancer treatment are often counseled about fertility preservation options like egg or sperm freezing before therapy begins.
Other Medical Treatments and Medications
Cancer treatment isn’t the only medical cause. Hormone therapies used for conditions like endometriosis or breast cancer can suppress ovulation. Certain antidepressants, antipsychotics, and blood pressure medications can raise prolactin levels enough to interfere with fertility. Long-term use of high-dose anti-inflammatory drugs may affect ovulation. In men, testosterone replacement therapy and anabolic steroids can shut down the body’s own sperm production, sometimes for months after stopping.
Weight and Lifestyle
Body weight sits at the intersection of several fertility pathways. Being significantly overweight or underweight disrupts the hormonal balance needed for regular ovulation. Obesity worsens insulin resistance, which compounds the effects of PCOS. In men, excess body fat is associated with lower testosterone and reduced sperm quality.
Smoking damages fertility in both sexes. It accelerates egg loss in women, reduces sperm counts in men, and lowers IVF success rates. Heavy alcohol consumption and recreational drug use also impair reproductive function.
When Fertility Testing Is Recommended
The general guideline is to seek evaluation after 12 months of regular unprotected intercourse if you’re under 35, or after 6 months if you’re 35 or older. For women over 40, earlier evaluation is appropriate. Testing should begin right away, regardless of age, if you have irregular periods, a known history of endometriosis or pelvic disease, suspected male factor issues, sexual dysfunction, or any condition that might reduce ovarian reserve. Both partners should be evaluated simultaneously, since male and female factors coexist in a large percentage of cases.