Final answer:
Regular sunscreen use is the healthiest habit for protecting skin against the harmful effects of UV radiation from the sun and tanning beds, which can lead to skin cancer.
Step-by-step explanation:
The healthiest habit for the skin in relation to sun exposure is C) Regular sunscreen use. Sunscreen and sunblock protect the skin from the harmful effects of UV radiation, which can lead to skin cancer. While some sunlight is necessary for the production of vitamin D, excessive sun exposure without protection can cause sunburn and increase the risk of skin cancer. Tanning beds are also harmful because they expose the skin to UV radiation, which is a known carcinogen. The body does have a natural defense mechanism of tanning, which produces melanin to block UV penetration, but it is not adequate to prevent all UV damage.