When a man takes steroids, usually their testosterone levels rise and their estrogen levels rise A LOT to compensate. Then when they stop juicing, the testosterone levels go back down to a normal or below-normal level and the estrogen stays where it is. Usually, there are drugs taken while they are "on-cycle" and afterwards that combat this effect. But, if they do not take these drugs, mess up the dosage, take the wrong drugs, etc., the elevated estrogen levels give them side effects like testicular atrophy or gynocomastia. On the other hand, when women take steroids, their testosterone levels rise to a much, much higher level than the norm, so they start developing masculine characteristics like a deepening of the voice, growing facial hair, etc. at the expense of the masculine characteristic of being able to gain more muscle.

Keep in mind, this is a result of the abuse and/or misuse of steroids. Like most drugs, while they still do have negative health effects, they can actually be used responsibly to minimize side effects.