Help please! Is crest 3d white mouthwash antiseptic?

YES! Does it prevent the growth of disease-causing oral microorganisms? Hydrogen peroxide, the active ingredient is an oxidising agent, disinfectant and deodorant. It is bactericidal with a wide spectrum of action. Side effect: whitening tooth enamel. Use twice daily after brushing for both the whitening and the antiseptic effect. Same active ingredient as their strips.
Yes - a little. It's kinda weak for an antiseptic. However you don't want to use a stronger antiseptic on a daily basis or you risk fungal overgrowth.
It is an oral rinse. With antiseptic properties for the oral cavity . Is it an antiseptic to use outside its given scope, the answer is no. Hope this helps.