Campus Queries is a series in which Daily Bruin readers and staff present science-related questions for UCLA professors and experts to answer.
Q. Why does the skin turn red and peel due to sun exposure?
A. Nearly half of all young adults get sunburned, according to a CDC survey. Roger S. Lo, a UCLA dermatologist, studies melanoma, a cancer often caused by repeated sun exposure.
There are two types of ultraviolet radiation: UVA rays and UVB rays. UVA rays often cause premature aging while UVB rays often cause sunburn and some skin cancers.
When UVB rays damage skin cells, the body responds with an inflammatory response, Lo said. Blood rushes to the afflicted area, causing the red color generally associated with sunburns.
“Inflammation makes anything red due to cells dying within a short period of time,” Lo said.
UVB rays can also cause cells to undergo apoptosis, or programmed cell death. Massive cell death can cause sheets of skin to peel off the body.
Humans have a natural defense to the harmful UV radiation in the form of melanin, which determines skin pigmentation, Lo said.
Melanin acts as an absorbent filter for UV radiation.
There are two types of melanin involved in skin pigmentation – eumelanin and pheomelanin – but only eumelanin is involved in protecting the skin from the sun.
People with a darker pigmentation tend to have more eumelanin, while people with fairer skin and red or blond hair tend to produce more pheomelanin and thus are at a higher risk for skin cancer.
“People with red hair and freckling skin are at a higher risk of melanoma. They not only have an inferior pigment but their pigment itself is a problem,” said Lo.
Constant damage to skin cells’ DNA by UV radiation can cause mutations in the DNA. This can lead to uncontrolled cell growth and mistakes in the DNA repair process which can result in cancerous cells.
Lo said that the most deadly skin cancer is melanoma, which is known for its dark-colored appearance. However, the most common types of skin cancer are basal cell carcinoma and squamous cell carcinoma.
Sunscreen contains inorganic and organic chemicals that deflect and absorb UV rays, respectively. The sun protection factor number found on sunscreen bottles refers to how long it will take one to get a sunburn. For example, someone wearing sunscreen with SPF 15 would get a sunburn 15 times slower than someone not wearing sunscreen.
An SPF 15 sunscreen can protect the skin from about 93 percent of UV rays, while an SPF 30 sunscreen can protect the skin from 97 percent of UV rays. No sunscreen can protect users from 100 percent of UV rays.