Masturbation relaxes you mentally and physically if you do not feel guilty. To avoid future problem, you may use lubricated hand, do not stop breathing and keep your perineum relaxed and do not do it in prone position as it would put pressure on the root of your genital organ.
Masturbating is perfectly safe and will do nothing to your body. As long as you're not spending hours a day doing it and letting it interfere with your job, social life or anything else then it's okay and normal.
Thanks for your kindness. Then if it doesn't shrink the body the what does it do to the body?
No. It will not shrink your body.