Gyno, short for gynocomastia is what forms as a lump beneath the nipple. it's not necessasrily sides of steroid but it is highly possible.

let me explain this in the reverse manner.

gyno is caused by the binding of free moving estrogen in the male body with the receptors beneth the nipple forming disc like lump. do remember male bodies have estrogen too. in a certain proportion to testosterone. and the body keeps the balance of the proportion by having an enzime called aromatase which converts the excessive test to estrogen to keep the balance. this conversion is called aromatization.
this sometimes happens during puberty too because of the test spike in the body. doctors seem to believe there no prevention to this unless when the lump is too big and starts givin pain, gotta go under the knife(eg. Dwayne 'The Rock' Johnson) .

but if u can sense the gyno symptoms early enough, u actually can prevent it from it getting any bigger. symptoms are, intchy or sentisitivity in the nipple area.
u can start on arimidex an AI(aromatase inhibitor). what it does is, it inhibits the aromatase enzime in body which makes the aromatase to be unable to convert anymore test into estrogen. the symptom will subside in less than a day. u can run the course for a couple of day. and then u'll be just fine.


when i said this may occur during puberty, not for every individual. some unlucky ppl as myself have higher amount of aromatase in our body. the amount of aromatase in the body in different from individual to individual. u're born with it and have pretty much have no control over it. so u gotta live with it.

that why everytime i get on a test base cycle i always have arimidex or letrozole or nolvadex in hand just in case. and i have to pretty much use it everytime too. it dies two things:
1) it prevents gyno and keeps the estrogen level in check
2) it actually increases the efectiveness of test because none is converted into estrogen and the level of test will not drop.

i hope these info helps.


p.s. theres also another sides caused by estrogen . it's called Benign prostatic hyperplasia (BPH). arimidex can also help is this case.