I have a 4 week old baby. how do you know when they have a cold as opposed to normal newborn congestion?

?irritants?: The first months are troubled by narrow nasal passages & exposure to dust, fragrences, smoke & other irritants.Baby tries to flush these out of the nose with mucous but this often ends as congestion &cough.It also produces rattling with breathing. The best rx is washing out the nose with saline &suctioning the remainder. Eliminate irritants from babies environment & this will happen less.