In a study discussed in the December 2009 edition of the Archives of Dermatology, it was proven that smoking and unprotected sun exposure are the two main causes of premature aging. The strength in this study lies in its use of twin pairs, since using twins in an experiment controls for genetic predisposition. By controlling behavior variables like food and drinking consumption, the study is able to isolate the behavior it wants to study. In this case, it is whether unprotected sun exposure will make a person look older than the other. The study brought together 65 sets of twins who were examined by medical investigators and demonstrated that both smoking and unprotected sun exposure both cause premature aging of the skin and make you look older.
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