Go to the vet as fast as you can. It can kill the dog. Not only
the chemicals are harmfull. The dog can't digest the cotton wool.
Even if he doesn't show any signs right after he has eaten the
cotton woll. IT can harm the stomach or the digestive system later.
And it might be to late then.
The Westminster Kennel Club All Breed Dog Show is by far the
most famous dog show in the world. The Westminster Dog Show started
in 1877, and just completed their 137th annual show.
No cotton is not poisonous to your dog. However if they persist
on eating it then it can clog up the intestines. Also some dogs
(like people) can be allergic to cotton.
This varies drastically by the type of dog you have, the age of
your dog, etc. Months and months of preperation goes into getting a
dog ready for a show career.