Skin cell serves a completely different purpose. Muscle cells have large amount of mitochondria in them and are energy rich to perform functions that require movement. They are more durable than epithelial cells. Epithelial cells (skin cells) are quickly shed, quickly replaced, lack mitochondria and are mass produced by the body.
It depends on the context. It it looks like (H+) then it's an element with a positive charge. But if it looks like this ( N + 3O) then they are simply elements being combined (added) in a reaction.
debris from the volcanic ash has covered the sun which makes the temperature cold.
Rara tee da goo boo boo teee gaaa baa baa