It is profoundly ironic: to protect yourself in order to remain capable of hurting yourself.
In the end, self-harmers do what they do out of one or more of three reasons: They do it because they think they deserve it, and that stems from guilt and shame; they do it because they derive sexual pleasure from it, and that is self-explanatory, or they think that self-harming gives them control of their life back, and that comes from profound insecurity.
Two of those options stem from a history of abuse. Self-harming for sexual pleasure is relatively harmless, as S&M practitioners take very good care of themselves.
Do not hide your self-harm. You are either doing it to punish yourself, to control your life, or because you get off on it. From the way you worded your question, I am going to rule out the option of sexual gratification.
So ask yourself why you do it. Do you think you have to to control your life, or are you afraid that you deserve it? Neither one of those are healthy, but in admitting which one it is, you take the right step towards recovery.
Admit your self-harm to your parents and get the help you need, before you get too upset and cut yourself too deeply, or you catch an infection, but stop defending your self-harm.
Never forget that you matter, and you are not alone.