Breast growth also can be spurred in adult men by the use of certain prescription or over-the-counter medicines or illegal drugs like marijuana and steroids.
Sometimes gynecomastia's root cause lies in the genes (interactive genetics overview).
"There are genetic conditions [that cause more severe gynecomastia] sometimes you see breast enlargement in a young person from grandfather to father to child. That can be embarrassing and difficult to deal with," Spack noted.
Liver problems can also lead to gynecomastia, because the organ is unable to metabolize estrogen effectively.
"That's a setup for the adult to get gynecomastia," Spack said.
In the obese, pure fat can be misconstrued as breast glandular tissue, creating a similar appearance with a different cause.
Gynecomastia can cause physical issues, including painful hypersensitivity, but it is generally harmless.
Sufferers are more often prone to emotional and psychological problems resulting from what they perceive as an emasculating condition.
"We don't talk about things that men may not see as masculine," Yost said. "This is tantamount to saying that you're not a man for a lot of guys."
In private, however, many men are searching for help.
Yost, who runs his own psychotherapy Web site, added a gynecomastia forum page in 1997.
The page received such overwhelming traffic that he spun off a full information and resources site three years later, where he has gathered enormous amounts of feedback.
He explains that while many men are disturbed by gynecomastia, "there are as many responses [to the condition] as there are people."
"A man's response to gynecomastia often has as much to do with his partner's response as it does his own feelings," Yost said. "If the primary partner is embracing [the patient's] chest, it may diminish that negative response."
For those men who hope to treat their condition, they must first identify its cause. Some can gain relief by losing weight or altering their medications.
Spack, of Children's Hospital, believes that some prescription medicines could block the formation of estrogen and reduce breast size, but such treatments haven't been generally used in the U.S.
Timing is also a drawback: The drugs would only be effective early in the condition's development, but embarrassed sufferers rarely seek help at that stage.
For many men with gynecomastia, surgery may be the only solution.
Yost opted for the procedure, though he cautioned that many patientsincluding himselfhave reported less than satisfactory results.
Many surgeons are not accustomed to the procedure, he says, and he suggests that potential patients do their homework and find an experienced doctor.
Cost can be another drawback, Spack explains.
"One big problem is that it's hard to fight for this to be covered by insurance, because it's regarded as cosmetic," he said.
"But it's really awful for some of these kids who never take their shirt off at the beach or are tormented at school."
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