Black skin

Question
My dog is a Chihuahua mix, he has a very large black spot on the back, start from botton of the tel to olmost to de neck, looks like a big almond shape. Start two monto a go with a rash and turn to a big and crosty  black spot, very eachy he ust to scrash a lot. The eachy stops.but now only the big black spot.
Yesterday a foun out that some more black spots on the top of the ears, betwin the eyes and a medio of the tiel.
I don't know what to do. Can you help me please ?  Thank you.  Josefina

Answer
Your dog truly needs to go see a veterinarian. This is not something that can be done online.

Most likely he has a very bad flea allergy and he needs medication for the allergy as well as flea treatments.

Please call your vet and make an appointment for him today or tomorrow.