Which factor is responsible for 80% of skin changes in adulthood?

A) use of moisturizers
B) birth control pills
C) cigarette smoking
D) exposure to the sun

Exposure to the sun is responsible for 80% of skin changes in adulthood, including wrinkles, age spots, and skin cancer. It is important to protect the skin from UV radiation by wearing protective clothing, using sunscreen, and avoiding direct sunlight during peak hours. The other options, such as moisturizers and birth control pills, may have some impact on the skin but are not the primary factor in skin changes. Smoking is also harmful to skin health, but it contributes to a smaller percentage of skin damage compared to sun exposure.