Hi.. Can understand your concern.. As per your complain it seems that you are allergic to any of the component of toothpaste and although you have changed the toothpaste there are certain components which are common in all toothpastes like fluoride,sodium lauryl sulphate etc and when when you are exposed to them it leads to allergic reaction in the form of sneezing.. I would suggest you to use herbal toothpastes which does not contain fluoride,gluten,sweeteners dyes ,preservatives etc and can hopefully be helpful in preventing your allergy.. Few herbal tooth pastes are:Auremere ayurvedic herbal toothpaste. Weleda s Salt Toothpaste.. Kiss My face triple action whitening etc.. Hope this information helps.. If you find the answer helpful please write a positive review and click on find this answer helpful as a token of appreciation.. Thanks and regards.. Dr.Honey Nandwani Arora.