Growing up, your mother probably told you to eat the skin of your potato. The nutritious skin is where a lot of the vitamins are. Important nutrients such as fiber, calcium, iron, and vitamin C are found in the skin. However, you probably didn't know that potato skins contain poison.
Believe it or not, potatoes are part of the deadly nightshade family. They defend themselves against ravaging bugs by producing a toxic chemical called solanine. As defenses, they are only useful to the potato by being concentrated in the peel.
Though it wars off some bugs, the amount of solanine in a potato skin is harmless to people. That is, unless it's been exposed to too much sunlight. Sunlight can cause an increase in solanine levels, and then you should indeed stay away from eating the skin. Fortunately, when this occurs, the potato skin turns green. If the skin is green, don't eat it.