Why do they have expired label on foods and what will it cause if someone eat an expired food?

Expiration dates are used to indicate how long foods are considered to be safe for. After that date, there is a chance that the food will have spoiled. If it has spoiled, there is a possibility of illness, such as food poisoning. If it hasn't spoiled, there won't be a problem. Some expiration dates deal with how long the flavors will last without going 'off' and tasting funny.