verysummer,millions of Americans flock to beach-
es with the dual goals of having fun in the sun and
getting that ideal symbol of beauty, the perfect suntan.
The quest does not end at the beach. Many people, es-
pecially teens, use indoor tanning devices. The Centers
for Disease Control and Prevention (CDC) estimates that
in 2005, 8.7% of teens aged 14 to 17 used indoor tan-
ning devices. According to that report, girls are seven
times more likely than boys to use tanning devices.
However, exposure to ultraviolet rays, whether from the
sun or a tanning bed, causes both tanning and sunburn.
In the same report, the CDC noted that the prevalence
of sunburn among adults is on the rise. From 1999 to
2004, the percentage of sunburned adults rose from
31.8% to 33.7%.
Sun exposure causes skin damage and is an impor-
tant risk factor in skin cancer, most commonly basal cell
carcinoma and melanoma. These types of skin cancer
are also on the rise. In 2009 (the most recent year for
which statistics are available), 68,720 people in the
United States were diagnosed with melanomas, and
8,650 people died from this deadly type of skin cancer.
Let's look at the structure and function of skin and
see how environmental factors affect it.