Well, masturbation or sex will not cause the body any physical harm, including hair loss. Perhaps few pubic hair might be lost during the sexual activity, but it generally grow back.
Everyone experiences some hair loss daily, up to 100 hairs per day. Excessive hair loss can be caused by many factors such as genetics, disease, injury, or old age, any disease or illness, all of which affect the normal growth cycle of hairs.
There is only a problem with frequency of masturbation when it begins to interfere with daily activities or is causing emotional distress. As long as you can continue to function in your daily activities such as school, job, studying, family, etc., there is not a problem. Masturbation is a healthy sexual outlet.