Pedigree dogs have different behavioral and physical characteristics among them, for these reasons their future mates-owners should consider all the causes determining it, avoiding this way dissatisfactions or problems which can lead to the abandonment.
There are some races, generally bulldogs, mastiffs, but even smaller sized ones, who have a particular structure of the face for which they “drool” much more than others. In this case it is not a pathology but only a characteristic that can become bothersome both for the domestic management and for the hygiene and cleanliness of the same subject.
The appearance of the drool in races or subjects who are not predisposed is different: in this case it could be a symptom of some pathologies, it appears only on one side, for causes linked to dental, salivary, tongue and tonsil pathologies. Or because of poisonings, allergies to medicines: in this case it appears suddenly. The aspect can be very different, clear like salive or more compact similar to mucus, even rose colored for the presence of small bleedings.
If a sudden “scialorrea” appears, before opening the mouth to our dog, I suggest to wear latex gloves, to verify the condition of teeth and mouth in general (sometimes there could be only an unrelated object stuck in the mouth, slivers of wood and bones easily removable); if the problem were not so easily resolvable instead, contact your veterinary doctor the soonest.