Why my Gynecomastia Looks More Obvious After Masturbation or Marely Even Sexual Excitment?

my gynecomastia looks like its pure, and its been 10 years now, it hasn't gone.i m 28 years old. and whenever i feel sexually excited i get this feeling that something is surging and stimulating the gyno, if done masturbation the gyno increases, and if i refrain from sexual activity, it becomes relaxed, but a mere feeling of sexual excitement makes it worse. i have it on right side of my chest and i m not obese.and never took steroids. its not very large in size but prevents me from wearing t shirts.