My female dog has a small lump on her inner thigh and I don't know what it is. She responds with yelping and squirming when I touch it, and it has recently developed a black tip on it. It is slightly squishy, but mostly hard. It's not a nipple because her other ones are dark brown.
Ultimately it's impossible for us to tell what this is without physical access to the dog. The only one who could tell for sure is a local vet.
The possibilities range from a benign skin tag over an infection to skin cancer.
There's a similar question over at PetCoach and the answer includes:
Be sure to visit your local Veterinarian as soon as possible and request a Fine Needle Aspiration. This will allow your doctor to rule out the presence of any infection or cancerous cells.
