A celebrity is a person who has achieved fame, usually in the fields of movies, music, writing or sports. A celebrity's fame usually stems from a combination of factors such as high visibility, success in the field and popularity, a large following or a positive public image. Many people who achieve celebrity status are able to combine this with a stable and lucrative career. Celebrities can be a positive influence on their audiences as well as negative, as shown by some celebrities who use their fame for questionable purposes or those who treat others badly in order to increase their own popularity.While there is plenty of evidence to suggest that people trust celebrities when it comes to health issues such as body image and cancer screening, there is a lack of research that examines how celebrity influences these factors. A planned systematic review and meta-analysis of the existing evidence is needed to measure the magnitude of celebrity influence in different contexts, populations and outcomes.In the past, there was a distinction between being famous and being a celebrity. A person could be famous for winning a Nobel Prize, publishing an important book or being an excellent athlete without becoming a celebrity. Today, there is a more fluid definition of what constitutes celebrity. People who are famous for being funny, interesting or attractive often become celebrities, as do people who have a lot of money and those who are very good at what they do, such as movie stars and musicians. Even saintly individuals such as Mother Teresa have sometimes achieved celebrity status.There is also a difference between celebrities who are well known and those who are talked about. A celebrity who has a huge following and is known worldwide is generally considered to be much more recognizable than someone who is simply well-known. Some individuals achieve celebrity status because of the significance of their family name, such as members of royal families or artistic dynasties like the Barrymore and Cassidy (David and Shaun) families.A celebrity can be a positive influence on the audience by promoting good values or by encouraging them to follow their dreams. However, a celebrity can also be negative by exposing the flaws of society, showing the bad side of human nature or causing trouble in their personal lives.A celebrity can be a positive influence on society by teaching healthy lifestyles, such as eating right and exercising regularly. They can also be a negative influence by using their status to promote poor behavior, such as smoking and drug abuse. Celebrities can also encourage a voyeuristic mindset in the audience, which leads to people feeling as though they are entitled to see celebrities doing normal things such as taking a shower or buying groceries. This type of narcissism can lead to depression and social isolation. This is why it is important for celebrities to carefully balance their public and private lives.