Is diarrhea a symptom of teething?

As Hui Qun has mentioned, there isn't any scientific linked between teething & diarrhoea. If you suspect that your child is teething (see Hui Qun's comments for signs), you can offer him teethers to sooth his gums. For me personally, my son like gnawing on his cloth books that came with teething edges as well. I got a few of these cloth books at the January babyfair at about $8 each and he absolutely loves thema!