Sons of men and women who have who have been diagnosed with breast cancer or who have BRCA1 or BRCA2 mutations are at higher risk for breast cancer than the general population. Parents have little control over many risk factors, such as an undescended testicle, Klinefelter's syndrome, CHEK2 mutation, and Cowden syndrome.
There are other risk factors parents can influence. These generally fall under diet and lifestyle factors, although minimizing exposure to certain pollutants and ionizing radiation are also important.
Given the similarities between male and female breast cancer, it may be that steps shown to prevent breast cancer in girls may also be useful in preventing it in boys. However, we will only be discussing factors that have been shown specifically to influence male breast cancer risk in this webpage.

Protecting our sons from breast cancer during infancy

Parents should limit using baby care products containing lavender or tea tree oil, which have been shown to produce estrogenic effects in boys, and parabens, which are suspected to interfere with male reproductive functions. In addition, herbal treatments for colic containing fennel (Foeniculum vulgare) should not be used since they may cause premature breast development in babies. Also to be avoided are clear plastic baby bottles, sippy cups, and toys containing polycarbonates, which have been shown to be carcinogenic. Plastic products containing polycarbonates may be marked on the base with a triangle containing the number 7.
Soy infant formula contains phytoestrogens that have been shown to delay puberty in male rats. While the few studies that have compared the health of milk formula-fed children with soy formula fed children have not reported adverse effects for soy, based on the available evidence, boys fed soy formula could suffer from subtle demasculinization effects.
Boys should be vaccinated against mumps to prevent possible damage to the testicles associated with mumps.

Childhood exposure to oncogenic viruses

Certain viruses have been reported to be associated with breast cancer. These include mouse mammary tumor virus (MMTV), bovine leukemia virus (BLV), Epstein-Barr virus, human papilloma virus (HPV), human cytomegalovirus (Human Herpes virus 5), and measles virus. The topic is controversial, in part because of problems with methodology and inconsistent findings. In any case, it makes sense to reduce or avoid exposure to these viruses.
Steps should be taken to avoid transmitting herpes to children during pregnancy or childbirth. Boys should be vaccinated against measles as young toddlers and HPV as older children. Children should not be served raw milk and uncooked beef, both of which are possible sources of BLV infection, as noted above. Although it is possible that MMTV is more often transmitted between humans rather than being passed directly from mice, it makes sense to avoid exposing children to mice, including pet mice.

Some personal care products contain endocrine disruptors

Some personal care products have been found to cause signs feminization, including the development of breasts, in boys. These include shampoo and other hair products, body creams, body oils, and other personal care products containing lavender, tea tree oil, or parabens. Sunscreens and other UVF-rated personal care products containing benzophenones, octylmethoxycinnamate, 4-methylbenzilidenecamphor or homosalate should also be avoided. These products all are intended for external use, but are absorbed through the skin or scalp. In addition, there are a number of hair care and other products marketed to African-Americans that contain placenta or “hormone” that should not be used to groom boys.

Childhood weight and exercise and subsequent breast cancer

Being overweight has been found to be associated with increased risk of breast cancer in adult men whereas physical activity is inversely related, even after adjustment for body mass index. It is not clear at what point in life overweight becomes a significant risk factor for subsequent breast cancer in men. However, since adult obesity often follows childhood obesity, it makes sense to take steps not to overfeed boys and to encourage daily physical activity. Since testicular injury is suspected of contributing to some cases of breast cancer, boys should wear athletic supporters and cups, as appropriate, for any sports in which they engage.

Childhood radiation treatment increases breast cancer risk

Whether used to treat or to diagnose illness, radiation to the chest or back (including x-rays, CT scans, and radiation treatment) during childhood can result in breast cancer in adulthood. While such radiation normally is administered for medically necessary reasons, parents of boys at high risk for later breast cancer should pay attention to the degree of exposure and try to limit it, where possible. Parents should also make sure that the chest is fully protected when radiation is administered to the head or neck or other areas close to the chest or back.

Childhood diet

Although there is ample evidence that diet can influence risk of breast cancer in women, the evidence is thin for men. Consumption of red meat has been associated with increased male breast cancer risk in several studies, and intake of fruits and vegetables with reduced risk. One 2021 study reported that consumption of tree nuts is associated with a lower risk of excessive estrogen (hyperestrogenism) in men. Factors that affect breast cancer risk in men may begin to contribute to risk starting in childhood.
Men diagnosed with estrogen positive disease might consider reviewing our article on what to eat for hormone receptor positive breast cancer in women to examine the possibility that the family diet might increase risk of breast cancer in their sons.

Exposure to environmental carcinogens

Some plastics contain estrogenic and otherwise carcinogenic chemicals that can leach into food when the plastics are heated, microwaved, put under pressure or simply scuffed and worn. These chemicals include bisphenol A (BPA), styrene, and phthalates. Plastics that may leach these substances include (1) polyvinyl chloride (PVC), which may be found in cling wrap, some plastic squeeze bottles, and cooking oil bottles; (2) polystyrene, which may be found in styrofoam food containers and disposable cups and bowls; and (3) polycarbonates, which may be found in soup and soda can linings, plastic baby bottles, water bottles, and clear plastic sippy cups.
Children and adults alike should avoid all but temporary, low temperature uses of these products. Plastic containers may be marked with a number in a triangle-like icon. Plastics marked 1, 2, 4 or 5 use less toxic additives in their manufacture. Products that use polyvinyl chloride should be marked with 3, polystyrene with a 6, and polycarbonate with a 7 — these are the ones to avoid.
Boys who are raised on or near farms, raised by farm workers, or who are themselves farm workers may be vulnerable to the breast cancer-promoting effects of certain hormones and other chemicals used in the production of food and other products. Boys should be kept out of harm's way when such chemicals are applied. This includes greenhouse crops. Parents of boys raised on or near farms should educate themselves on the risks of the specific chemicals used there and take appropriate precautions.
Household insecticides containing lambda-cyhalothrin should also be avoided, since this chemical has been found to have estrogenic properties, including promoting the growth of hormone receptor positive breast cancer cells in the laboratory.

Summer jobs can result in potentially harmful exposures

Men who have worked in blast furnaces, steel works, rolling mills have been observed to have a higher likelihood of breast cancer, suggesting that heat may promote breast cancer in men (in fact, occupational exposure to heat has been reported to be a breast cancer risk factor for women). Workers in machinery repair, welding trades, and manufacturing of motor vehicles also have higher risk, indicating that exposure to environmental carcinogens such as polycyclic aromatic hydrocarbons, nitrogen oxides, nitrosamines, and metal fumes in some manufacturing environments are possible contributing factors. Some military bases also have unusually high rates of male breast cancer. High-risk teenagers should avoid summer jobs involving exposure to high heat or work environments likely to result in exposure to carcinogens. These factors should also be taken into account in selecting future careers.

Body building and weight loss products

Care should be taken in selecting any body building or weight loss products. For example, some protein powders consist primarily of soy protein, which is estrogenic as a result of its phytoestrogen content. Supplemental human growth hormone might also contribute to breast cancer risk. This is because tall height is associated with increased risk of male breast cancer, suggesting that high circulating levels of hormones that contribute to tall stature may promote breast cancer. Long-term use of antiperspirants or deodorants containing aluminum salts such as aluminum chlorohydrate could also increase the risk of breast cancer, especially if applied after shaving or when the armpits are irritated.

Sex change

The treatments required to induce male-to-female sex change, including castration and large doses of female hormones, lower androgen levels and increase the estrogen-to-androgen ratio, thereby increasing the risk for breast cancer. Those undergoing sex change should be made aware of the increased risk of breast cancer and be screened for it periodically.

Breast self-exams

Since men are typically not screened with mammograms, they usually find their breast cancers themselves. Higher risk teenagers should be taught to perform breast self-exams. Adding this instruction to a lesson on testicle self exam might make it more palatable.

Additional comments

Fathers and mothers who themselves have an elevated risk of breast cancer might benefit from eating a wide variety of the foods on our recommended food list and limit or avoid those on our avoid list, in addition to paying attention to them when providing meals for their children.
Below are links to 20 studies concerning this topic. For a more complete list of studies, please click on prenatal exposure or protecting our children.