The sun's ultraviolet rays help the skin produce vitamin D, a nutrient that is essential for strong bones and overall health. When skin is exposed to sunlight, it triggers a process that converts a form of cholesterol in the skin into vitamin D3. Vitamin D is also known to have important roles in the immune system, brain function, and muscle function. However, it is important to balance sun exposure with appropriate measures to protect against skin damage and skin cancer. The American Academy of Dermatology recommends protecting the skin by seeking shade, wearing protective clothing, and using sunscreen with at least SPF 30.