Old wives' tales are pieces of advice that are supposed to solve common problems such as the medical ones or some problems at home. They are usually passed down through talking，and there are only a few having been written down. Some of them sound ridiculous and have no scientific meaning at all，just like jokes，while others are more reasonable，which are realized to be true.
Often，old wives' tales take the form of warnings and are a way to prevent poor behavior in children. For example， "Eating candy before bedtime brings you bad dreams" is a common old wives' tale that was probably thought up to stop children from eating too many unhealthy snacks. Similarly， "If you've been lying，your nose will be longer" is a trick trying to get naughty children to tell the truth.
Other old wives' tales want to give advice about how to keep away from illnesses. "If you go outside with wet hair，you'll catch a cold" is an old wives' tale that's still commonly heard today. However，colds are not caused by cold weather or wet hair. Instead，they are caused by viruses （病毒）.
"Feed a cold，starve a fever" means that you should eat plenty of food when you have a cold，but not eat when you have a fever. This piece probably comes from the fact that people with a fever usually lose their appetite （胃口） anyway. Medical science has found that the body stops eating much when you have a fever because little food makes your immune system （免疫系统） fight bacterial infections （细菌感染），while eating a little more makes your immune system fight against viruses，like colds.
There are hundreds of old wives' tales. Although there may be truth in a few of them，if you bear one，it's best not to take it too seriously.
