The only firmly established environmental cause of brain tumors is exposure to moderate or high doses of ionizing radiation. Beyond that single clear-cut factor, risk is shaped by a mix of age, sex, genetics, family history, and certain chemical exposures, most of which raise risk modestly rather than dramatically. Here’s what the evidence actually shows.
Age and Sex
Brain tumor risk climbs steadily with age. The rate per 100,000 people roughly doubles with each decade of life after age 35, peaking in adults 75 and older at about 20 cases per 100,000. That said, brain tumors also occur in children and young adults, just far less frequently (about 3 per 100,000 in those under 15).
Men are diagnosed more often than women, accounting for roughly 56% of cases overall with a rate of 7.5 per 100,000 compared to 5.7 for women. This gap is driven largely by gliomas, the most common malignant type, which are more frequent in men. Meningiomas, which are usually benign, are more common in women.
Ionizing Radiation
Ionizing radiation is the strongest and most well-documented environmental risk factor. The evidence comes from two main populations: survivors of the atomic bombings in Japan, and people who received radiation to the head during childhood for medical conditions like scalp ringworm or childhood cancers. In both groups, brain tumor rates were significantly elevated years or decades later.
Radiation is more strongly linked to meningiomas than to gliomas. Children who received head radiation for ringworm treatment, for example, had roughly five times the expected rate of meningiomas. The younger you are at the time of exposure, the greater the risk appears to be for gliomas specifically. Diagnostic imaging like a single CT scan delivers a far lower dose than therapeutic radiation, but repeated scans to the head during childhood are still something doctors try to minimize.
Family History and Inherited Conditions
Having a first-degree relative (parent, sibling, or child) with a glioma roughly doubles your own risk of developing a brain tumor. That sounds alarming, but context matters: the baseline risk is low, so doubling a small number still leaves you with a small number. The vast majority of brain tumors occur in people with no family history at all.
A few rare genetic syndromes carry much higher risk. Neurofibromatosis types 1 and 2 are caused by mutations in tumor-suppressing genes and predispose people to nerve sheath tumors and sometimes gliomas. Li-Fraumeni syndrome, caused by mutations in a key cell checkpoint gene, raises the risk of many cancers including brain tumors. Tuberous sclerosis and Turcot syndrome are two other inherited conditions linked to brain tumor development. Together, these syndromes account for a small fraction of all brain tumors, but if your family has a pattern of unusual cancers diagnosed at young ages, genetic counseling can help clarify your situation.
Occupational and Chemical Exposures
Certain workplace chemicals have been linked to higher brain tumor rates in studies of occupational health. The most consistently reported associations involve pesticides, formaldehyde, vinyl chloride, lead, solvents, and petroleum products. Workers exposed to combinations of these chemicals alongside strong electromagnetic fields may face a compounded risk, though teasing apart which exposure matters most is difficult.
For most people outside of agricultural, industrial, or manufacturing settings, these exposures are minimal. If you work regularly with pesticides or industrial solvents, using proper protective equipment is the most practical step you can take.
Cured Meats and Childhood Brain Tumors
One dietary factor has drawn consistent attention: a mother’s consumption of cured meats during pregnancy and the risk of brain tumors in her child. Cured meats like hot dogs, bacon, and deli meats contain compounds called N-nitroso compounds, which are known carcinogens in animal studies. Most epidemiological studies examining this link have found a significant positive association between maternal cured meat intake during pregnancy and childhood brain tumor risk. The specific compounds thought to be responsible are N-nitrosamides, which can act directly on cells without needing metabolic activation.
For adult brain tumors, the dietary picture is much less clear. No specific food or nutrient has been convincingly shown to raise or lower risk in adults.
Cell Phones and Radiofrequency Fields
The International Agency for Research on Cancer classifies radiofrequency electromagnetic fields, the type emitted by cell phones, as “possibly carcinogenic to humans” based on limited evidence of a link with glioma and acoustic neuroma. That classification has remained unchanged through 2025. “Possibly carcinogenic” is the agency’s third tier out of four, meaning the evidence is not strong enough to confirm a real effect but not absent enough to dismiss it. Large studies have produced conflicting results, and no mechanism for how low-energy radio waves could damage DNA has been established. If this concerns you, using speakerphone or earbuds reduces exposure to the head, but the current evidence does not support treating cell phones as a proven risk factor.
Allergies and Immune Function
One of the more surprising findings in brain tumor research is that people with respiratory allergies, asthma, or eczema appear to have a lower risk of developing gliomas. The Glioma International Case-Control Study, one of the largest investigations of this question, found that respiratory allergies were associated with about a 30% reduction in glioma risk. Asthma was tied to a 23% reduction, and eczema to a 29% reduction. These findings align with multiple earlier studies and three separate meta-analyses, all estimating a 20 to 40% lower risk among people with allergic conditions.
The leading theory is that an overactive immune system, the kind that produces allergy symptoms, may also be better at detecting and destroying abnormal cells in the brain before they can form a tumor. This doesn’t mean allergies are protective in any way you could engineer, but it does highlight how immune surveillance plays a role in whether tumors develop.
Viral Connections
Cytomegalovirus, a common virus that infects the majority of adults worldwide without causing obvious illness, has been detected in over 90% of glioblastoma tumors and a similarly high proportion of medulloblastomas. Researchers have identified specific viral proteins inside these tumors that appear to promote blood vessel growth, cell migration, and inflammation, all of which help tumors thrive. Whether the virus actually helps cause the tumor or simply thrives in tumor tissue remains an open question. Early clinical work at Karolinska University Hospital in Sweden found that glioblastoma patients who received antiviral treatment alongside standard therapy had dramatically better survival rates, but these results need confirmation in larger controlled trials before drawing firm conclusions.
What You Can and Cannot Control
Most brain tumor risk factors, like your age, sex, and genetics, are not modifiable. The factors you can influence are relatively narrow: minimizing unnecessary radiation exposure to the head (especially in children), reducing contact with industrial chemicals through proper workplace safety, and for pregnant women, being mindful of cured meat consumption. Beyond that, brain tumors remain one of the cancers where the causes are least understood and hardest to prevent, which is precisely why researchers continue to study immune function, viral involvement, and environmental exposures for clearer answers.