The primary effects of ultraviolet radiation or tissue exposure are

• A. Photochemical
• B. Production of vitamin D
• C. Both A and B
• D. Neither A nor B

Answer: (A)

Ultraviolet exposure drives immediate chemical changes in tissue from the energy it delivers. When UV photons are absorbed by molecules like DNA and other skin chromophores, they can cause photochemical alterations—new bonds form or bond breaks occur, leading to molecular changes that can trigger cellular responses or damage. These rapid, direct chemical effects are what we mean by photochemical changes, and they are the primary result of UV exposure on tissue.

Producing vitamin D is a specific downstream outcome of UV exposure: a photochemical reaction in skin cholesterol (7-dehydrocholesterol) converts it to previtamin D3 and then vitamin D3. While important, this is a secondary biochemical consequence rather than the immediate tissue-change effect, so it isn’t the primary effect of ultraviolet exposure.