Most benign brain tumors have no single identifiable cause. They arise from a combination of genetic changes within specific cell types, and in most cases, those changes happen spontaneously rather than from something you did or were exposed to. Still, researchers have identified several clear risk factors, from inherited genetic syndromes to radiation exposure to hormonal influences, that meaningfully increase the odds of developing one.
How Benign Tumors Form Without Being Cancer
A benign brain tumor grows from normal cells that begin dividing in an uncontrolled way, but unlike malignant tumors, they don’t invade surrounding tissue or spread to other parts of the body. The most common types grow from specific support cells in and around the brain. Meningiomas, the most frequent benign brain tumor, grow from the membranes that line the brain. Schwannomas arise from the cells that produce the protective coating around nerves. Pituitary adenomas develop in the pea-sized gland at the base of the brain.
What triggers these cells to start growing abnormally is usually a mutation in one or more genes that control cell division. These mutations can be inherited, but far more often they occur on their own during a person’s lifetime. For pituitary adenomas, for example, the exact cause remains unknown in the vast majority of cases. Scientists believe that spontaneous changes in certain genes play a key role, but pinpointing the specific trigger for any individual tumor is rarely possible.
Inherited Genetic Syndromes
A small but well-documented percentage of benign brain tumors trace back to inherited conditions. The WHO currently recognizes at least 10 hereditary tumor syndromes that involve the nervous system, with several more recently added. These syndromes are caused by mutations in specific tumor-suppressor genes or growth-regulating genes that a person inherits from a parent.
The best known include neurofibromatosis types 1 and 2, which cause tumors to grow along nerves, and tuberous sclerosis, which triggers noncancerous growths in the brain and other organs. Von Hippel-Lindau disease predisposes people to tumors in the brain, spinal cord, and other areas. For pituitary adenomas specifically, the inherited conditions that raise risk include multiple endocrine neoplasia types 1 and 4, Carney complex, and McCune-Albright syndrome.
More recently identified syndromes include DICER1 syndrome, caused by a mutation in the DICER1 gene, and BAP1 tumor-predisposition syndrome, caused by mutations in the BAP1 tumor-suppressor gene. Carney complex, which has nearly 100% penetrance (meaning almost everyone who carries the mutation develops the condition), is driven by variants in the PRKAR1A gene. These discoveries are expanding the list of people who may benefit from genetic screening, particularly those with a family history of multiple tumor types.
That said, inherited syndromes account for only a minority of all benign brain tumors. Most people diagnosed with a meningioma, schwannoma, or pituitary adenoma have no family history of the condition.
Radiation Exposure
Ionizing radiation is the most firmly established environmental risk factor for benign brain tumors, particularly meningiomas. People who received radiation therapy to the head during childhood, often as treatment for another cancer, carry an elevated risk of developing a brain tumor years or even decades later.
The European EPI-CT study, which tracked cancer risks from CT scans in children and young adults, used a minimum five-year exclusion period after scanning to capture tumors that developed as a result of exposure rather than the condition being scanned for. Among those who developed brain tumors, the average cumulative radiation dose to the brain was 76 milligray, compared to 47 milligray in the overall study population. The long gap between exposure and tumor development is a hallmark of radiation-related brain tumors: they typically take at least five years to appear and often much longer.
Routine diagnostic imaging like a single CT scan carries a very small absolute risk. The concern increases with repeated exposures, higher doses, and younger age at the time of exposure, since developing brains are more sensitive to radiation damage.
Hormones and Meningioma Risk
Meningiomas occur roughly twice as often in women as in men, a pattern that pointed researchers toward hormones as a contributing factor. These tumors express receptors for both estrogen and progesterone, meaning they can respond to those hormones the way breast tissue does.
A large Danish study of nearly 790,000 women aged 50 to 60 found that menopausal hormone therapy raised meningioma risk. Women who used combination estrogen-progestin therapy had a 21% higher risk of meningioma compared to women who never used hormones. Progestin-only therapy carried a 28% increased risk. The type of regimen mattered too: continuous estrogen-progestin use (taking hormones every day without a break) was associated with a 34% increased risk, while cyclic use (taking hormones with periodic breaks) showed no statistically significant increase.
Current or recent progestin-only use showed the strongest signal, with risk estimates as high as 64% above baseline for meningioma, though the numbers were too small to reach full statistical significance. Previous use of combination therapy five to ten years before diagnosis also showed a meaningful association, suggesting that hormonal exposure can set changes in motion well before a tumor becomes detectable.
This doesn’t mean hormone therapy will cause a brain tumor. The absolute risk remains low. But for women with other risk factors, it’s relevant information to weigh.
Molecular Changes Inside Tumor Cells
At the cellular level, benign brain tumors are driven by mutations in signaling pathways that tell cells when to grow and when to stop. In children, low-grade gliomas (the most common pediatric brain tumors) frequently involve alterations in the MAP kinase pathway, a chain of proteins that relays growth signals from outside the cell to the nucleus. A specific gene fusion called BRAF-KIAA is one of the most common drivers, and newer targeted therapies that block this pathway have shown strong response rates in clinical trials.
Other pathways implicated in benign tumor growth include the PI3K pathway, which regulates cell survival and proliferation, and the CDK4/6 pathway, which controls how cells move through their division cycle. Understanding which pathway is driving a particular tumor is becoming increasingly important not just for diagnosis but for choosing treatments, as drugs that target these specific molecular errors can sometimes shrink tumors that would otherwise require surgery.
Why Benign Tumors Still Cause Problems
The word “benign” can be misleading. These tumors aren’t cancerous, but they grow inside a rigid skull with limited room. As a benign tumor expands, it compresses surrounding brain tissue and can raise pressure inside the skull. Even a small tumor in a critical location can damage the specific nerve pathways running through that area, causing symptoms like vision loss, hearing changes, or hormonal imbalances depending on where it sits.
Larger tumors can block the flow of cerebrospinal fluid, the liquid that cushions the brain and spinal cord. When fluid can’t drain properly, it builds up (a condition called hydrocephalus), further increasing pressure. Tumors also generate new blood vessels to feed their growth, and these abnormal vessels can leak fluid into surrounding tissue, causing swelling that adds to the pressure problem. In severe cases, rising pressure can push brain tissue out of its normal position, a dangerous situation called herniation.
This is why even noncancerous brain tumors often require treatment. The tumor itself may not be spreading, but its physical presence in a confined space creates real neurological consequences.
Cell Phones and Other Suspected Risks
Cell phone use is one of the most commonly asked-about risk factors, and the weight of evidence is reassuring. The National Cancer Institute’s current assessment is that cell phone use does not cause brain or other cancers in humans. Incidence rates for acoustic neuroma and meningioma, the two benign tumor types most scrutinized in cell phone research, have remained stable among U.S. adults since 2009, a period when cell phone use skyrocketed.
A few earlier studies reported a possible link between very heavy, long-term cell phone use and acoustic neuroma, but those findings haven’t held up. A study of over 264,000 participants with a median follow-up of seven years found no association between cumulative mobile phone call time and the risk of meningioma, acoustic neuroma, or glioma. A large Danish cohort study initially reported an association with acoustic neuroma, but the link disappeared with additional years of follow-up. The type of energy cell phones emit (radiofrequency radiation) is far weaker than the ionizing radiation from X-rays or CT scans and does not damage DNA in the same way.
Age and Gender Patterns
Benign brain tumors can occur at any age, but certain types cluster in specific groups. Meningiomas become more common with age and peak in people over 60. They affect women roughly twice as often as men. Pituitary adenomas are most frequently diagnosed in adults between 30 and 60. Pilocytic astrocytomas, the most common low-grade brain tumor in children, are typically diagnosed before age 20.
For brain tumors overall (including malignant types), the median age at diagnosis is 61. About 43% of new cases occur in people between 55 and 74, while roughly 10% are diagnosed in people under 20. These patterns suggest that accumulated genetic damage over a lifetime plays a role in many cases, though the childhood tumors driven by MAP kinase pathway alterations point to a distinct biological process that doesn’t depend on decades of cellular wear and tear.