Yes eating your own skin is cannibalism.
Eating your own skin is known as self cannibalism.
Eating your own skin is not good for your own health or your body because you destroy your skin but if you eat other peoples skin or do cannibalism with other peoples bodies it gets even more unhealthy and can be deadly.
Eating another humans brain can cause you to get a brain disease known as kuru.
The kuru is a brain disease that is similar to mad cow disease.
Brain disease Kuru occurs because our own brains contain prions that transmit the disease so when you eat another human brain you can get that disease and then die.
So eating a human brain or just eating any part of the human body can be dangerous to other humans health.
Symptoms of the brain disease which is known as Kuru starts with the body trembling and then it ends in death.
There's no cure for the Kuru brain disease and you will die once you get it.
Also unless you murdered someone or got their dead body somehow you would not be able to get the human brain to eat in the first place.
But if you killed the person which is illegal then you would go to prison for murder.