Baking potatoes in foil helps keep their skin soft and allows you to keep them warm for a while after you take them out of the oven, which is useful if you're not quite ready to eat them when they finish cooking. There are some drawbacks to using this method, though, including an increased risk for food poisoning, so you're better off cooking your potatoes another way.
Food Poisoning Risk
Botulism is a serious type of food poisoning that can cause death if you don't get treated right away. It causes difficulty swallowing, breathing and speaking, and symptoms typically appear between 18 and 36 hours after eating contaminated foods. The botulinum toxin spreads most in situations when there isn't oxygen present and can survive at the temperatures used to cook baked potatoes. There have been a number of outbreaks of botulism linked to potatoes baked in foil because the foil keeps oxygen away from the potato and allows the botulinum toxin to multiply.
Alzheimer's Disease Risk
Foil contains aluminum, which can potentially leach into foods and increase the amount of aluminum a person consumes. Although there is some controversy over the link between aluminum and Alzheimer's disease, there is a potential for aluminum to accumulate in brain tissues and increase the risk for Alzheimer's disease, according to an article published in the Journal of Alzheimer's Disease in 2011.
Other Potential Drawbacks
Baking potatoes in foil may also make it more likely you'll injure yourself. Because foil holds in moisture and steam, there's a chance of burns from the steam trapped inside the foil when you open the packet. Carefully open the packet so the opening is away from you to let the steam escape and limit this risk. Another option is to poke a few holes in the aluminum foil before baking so less steam remains in the packet.
You can bake potatoes in the oven without wrapping them in foil, although this will cause the skin to be crispier than when it's baked in foil. Another alternative that results in softer skin is to cook the potatoes in the microwave wrapped in paper towels. Regardless of the method you choose, scrub your potatoes and poke them a few times with a fork before you bake them, and turn them halfway through the cooking time to help them cook evenly.