otherwise travel to the lungs. Eyelashes shield eyes from dust and sunlight. Eyebrows stop
salty sweat and rain from flowing into the eye.
Keeping Skin Healthy
Some sunlight is good for health. Vitamin D is made in the skin when it is exposed to
sunlight. But, getting too much sun can be unhealthy. Asunburnis a burn to the skin
that is caused by overexposure to UV radiation from the sun’s rays or tanning beds. Light-
skinned people, like the girl inFigure16.10, get sunburned more quickly than people with
darker skin do. This is because melanin in the skin acts as a natural sunblock that helps
to protect the body from UV radiation. When exposed to UV radiation, certain skin cells
make melanin, which causes skin to tan. Children and teens who have gotten sunburned are
at a greater risk of developing skin cancer later in life than children and teens who have not.
Long-term exposure to UV radiation is the leading cause of skin cancer. About 90 percent
of skin cancers are linked to sun exposure. UV radiation damages the genetic material of
skin cells. This damage can cause the skin cells to grow out of control and form a tumor.
Some of these tumors are very difficult to cure. For this reason you should always wear
sunscreen with a high sun protection factor (SPF), a hat, and clothing when out in the sun.
As people age, their skin gets wrinkled. Wrinkles are caused mainly by UV radiation and
by the loosening of the connective tissue in the dermis due to age.
Figure 16.10: Sunburn is caused by overexposure to UV rays. Getting sunburned as a child
or a teen, especially sunburn that causes blistering, increases the risk of developing skin
cancer later in life. (^29 )
Because some types of skin cancer are easy to cure, the dangers of too much sunlight are
not always taken seriously by people. It is important to remember that a more serious
form of skin cancer, calledmelanoma, is also associated with long-term sun exposure.