Just drink pure lemon juice(without adding any other liquid) every morning b4 eating any food.(will not hurt your stomach because the P.H. point will change after that).Help in whitening skins and reduces oil on skins.
If you want better effect after getting the juice,use the lemon skin with water and rub your face during shower(do not just rub it on your face without water or you'll get rashes cause it's too strong) =D i drinks lemon everyday,warm my stomachs and no flu and pimple free~~