With regards to allergies, the Papillon may not be the most vulnerable of all the available breeds of dog, certainly, they are not nearly as sensitive as such other toy breeds as the Hairless variety of the Chinese Crested, whose bare skin leaves them especially open to the possibility of developing allergies to wool, but they aren't amongst the least sensitive, either and regardless, any owner of any animal absolutely must not neglect the obligation to know about any potential allergies that their dog might suffer from. Furthermore, the owner should make sure to be on the lookout for signs of these allergies in their pet and to make sure to double check product ingredients and not commit to any pet products that contain these allergens unless they are absolutely certain that they will not be putting the dog's comfort or health at risk.
Also to keep in mind is that an allergy is not necessarily a problem from birth and it might not develop until sometime later in the dog's life. A dog that has suddenly developed a habit of excessive scratching may be reacting to something that has never posed any sort of problem before. For this reason, Papillon owners absolute must be vigilant and knowledgeable, not just once, but throughout the dog's entire life.
A list of everything a Papillon might be allergic to would certainly be too long and unwieldy to place in the confines of this text, but some basic advice will fit just fine. Dust can be a problem, so a daily vacuuming routine may become a necessity. Mold spores are also a common allergy in all animals, so if your Papillon develops an unpleasant sneeze, he or she may be smelling something you don't, making a professional inspection necessary. Food allergies probably won't be much of a problem as long as the Papillon is being fed well on a specific, expertly recommended diet, but that doesn't mean a Papillon won't possibly be allergic to any of those recommended ingredients. In the event of a Papillon developing serious digestion problems, the owner might want to reevaluate the dog's diet. Basically, it's simply a good idea to pay close attention to how the Papillon reacts to various environments and influences.
Also to be considered, a lot of people are allergic to the dander or the fine hair of the Papillon. Any possible visitors should be informed that you have a toy breed with fine hair so that they can take the appropriate precautions should they suffer from such hypersensitivity.
Simply using common sense is probably the best advice. If your Papillon starts showing unusual signs of discomfort or seems to be unhealthy in some way, try to determine the cause of the problem. If it's an allergy, removing various influences and seeing how the dog reacts is an advised method of diagnosis. In the event of this method failing to root out the cause, a trip to the vet is probably in order.