The condition gynecomastia is defined as the enlargement of breast tissues in males. It can be caused by various factors, such as natural shifts in body chemistry. It also can be caused by man-made shifts through the use of anabolic steroids.
Marlon Byrd understands the assumptions -- that his gynecomastia is the result of steroids, that steroids are the reason he has revived his career and that he intentionally used a substance that has been banned because it masks this conspicuous side effect.
But in the 13 months that have passed since he received his 50-game suspension, the Mets outfielder has dealt with the constant suspicion by embracing it, especially now that he's in the middle of perhaps the best season of his career.
"I expected it," Byrd said. "The big thing is, why wouldn't anybody question it? I'm 35 going on 36. Last year, I hit .210 with a home run and [nine] RBIs, in conjunction with testing positive."
From the goading he hears from fans in the stands, to pundits online who are convinced that he is a cheat, doubt permeates Byrd's comeback story even as he maintains that he's never used illegal drugs to enhance his performance.
"I can take that and absorb that," he said of the lingering questions. "It doesn't bother me at all. But I guess you keep coming after a guy until they finally prove that they're clean. When does that happen? I don't know."
This year, his 17 homers rank eighth in the National League. The most he had ever hit was 20.
The timing of his resurgence also has generated whispers. It comes at age 35, a time when players often decline.
Yet another layer of doubt stems from his continued association with former BALCO mastermind Victor Conte, who after his federal prison stint has remade himself as a trainer and anti-doping advocate. Baseball has expressed its displeasure with the partnership. Nevertheless, Byrd still takes supplements provided by Conte, whom he trusts because he has "flipped to the good-guy side -- all out."
Even the original reason behind Byrd's suspension invites skepticism.
Byrd was a member of the Rangers when he first noticed that it hurt to slide headfirst. He eventually was diagnosed with gynecomastia, though he is unsure of the reason he developed the condition.
"Why that is, I have no clue," Byrd said.
He eventually underwent surgery to reduce the tissue in his breasts. When the condition cropped up again last year, he took the medication Nolvadex, hoping to prevent a relapse. He was unaware that Nolvadex contains tamoxifen -- a banned substance.
"It was me not doing my homework," said Byrd, who did not appeal his suspension.
After a terrible 2012 spent with the Red Sox and Cubs, Byrd spent his suspension in Southern California, where he worked on his swing. The one-time All-Star resurfaced in the Mexican League, where he wound up starring in the Caribbean Series, before catching on with the Mets.
Byrd said his turnaround came from efforts to fix his swing, not steroids.
He has been subject to additional tests for performance-enhancing drugs, a condition of his return after having tested positive, and he expects more before the end of the season. He doesn't mind.
Nor does he mind the questions, however uncomfortable or personal, even when they're about sensitive matters such as the growth of breasts. Byrd said the suspension remains "part of my history." So he answers the questions, knowing that some will never believe the responses.
He blames only himself.
"I'll tell you whatever you want to know. I have nothing to hide," Byrd said. "Of course, you use that quote and people are like, 'Oh, yeah, sure.' But I can only tell you everything about me. I'll be as forthright and as outgoing as I can."
It's part of the way he handles the scrutiny -- a side effect of his production.
"It's kind of weird," Byrd said. "But my goal should be to have people question me the rest of my career."