I think both pelo and cablello both mean hair, so what is the difference? When do you use one over the other? Is it a regional thing?
pelo vs cabello
I think you're right -- it's a regional thing.
While listening to Puerto Ricans and Colombians I heard them use "pelo" for the hair on your head and body.
While in Mexico a short while ago I was told to use "cabello" for hair on your head and "pelo" for hair on your body.
I noticed that all advertisements for hair products, like shampoo, use the word "cabello."
You may want to try this link and the next link indicated there to get a good answer to your question.
I think pelo is like a single hair / or the hair on say your arm and cabello is a head of hair.
Cabello is the hair on your head. Pelo is the hair of animals, and the body hair of humans. But, usually vello is the word that we use when we refer to our body hair. I hope this helps.