I do have serious catarrh each time i inhale dust from a counting machine.it is not frequent but it do happen until i take erithromycin.what is d caus?

Allergy: If one has serious sneezing or runny nose when inhaling dust, one could have allergies. The dust or dust mites (microscopic bugs that live in dust) could be triggering an allergic reaction. If by catarrh, one means "cough", then this could be due to allergic reaction of the lungs (asthma). In this case, one may need inhalers for asthma. Go see your doc, or an allergist.

Could be dust or...: Difficult to say. You should see sn allergist for a full exam.. And usually best not to take an antibiotic without seeing a dr.