What causes skin tags
Although it is generally unknown what causes skin tags some contributing factors that are believed could play a part are possible results of past damage, chronic trauma, skin infections, genetic factors or allergies.
How to identify a skin tag
Skin tags look similar to warts, they can grow anywhere on your dog's body. They tend to be thin and floppy at the base and are rounded or tear shaped, unlike warts they dangle from the skin and can be moved back and forth. They tend to be the same colour as your dogs skin.
What do to if you find skin tags
If they are small and don’t cause your dog any discomfort generally they can just be left, but if they change size or colour, get damaged or irritate your dog you should take them to the vet and possibly have them removed.
If skin tags appear around your dog's mouth or on his lips, they may be cancerous, or they may become cancerous. You should consult your vet if your dog develops them here.
There seems to be various methods available for removing a skin tag yourself at home, ie: tying it off. But the risks involved include infections, bleeding, pain and removing something that may have been cancerous that the vet would now not be able to check, thus preventing an early cancer diagnosis.
It is much safer to let the vet do this in a controlled environment. The options they have are cryosurgery, electrosurgery or to have it excised (cut out).