Discourages nail biting and thumb sucking nail biting is a nervous habit which can rapidly become uncontrollable mavala stop has a bitter yet harmless taste and the appearance of clear enamel it helps to break the nail biting habit and thumb sucking works for children more than 3 years old and adults how to use apply a coat over the entire nail or polish and allow to dry repeat the application every two days continue the treatment until nail biting has ended precaution never wash hands i