Question at position 14 Why does wearing sunscreen reduce cancer risk? It doesn't; sunscreen causes mutation and actually increases cancer risk.Sunscreen can reduce the chance of mutations caused by exposure to UV radiation present in sunlight.Sunscreen can repair damaged DNA.Sunscreen can activate checkpoints in skin cells.Sunscreen can prevent cells with mutations from being destroyed.Clear my selection

Question

BlackTom AI · Accepted Answer

Sunscreen absorbs and/or reflects ultraviolet (UV) radiation, reducing the number of UV photons that reach skin cell DNA and thereby lowering the probability that UV-induced mutations will occur.

1) Relevant knowledge points and concepts
- UV radiation (UVB and UVA) from sunlight can directly damage DNA (UVB causes cyclobutane pyrimidine dimers and 6-4 photoproducts) and indirectly cause oxidative damage (primarily UVA), both of which can introduce mutations.
- Accumulated mutations in proto-oncogenes or tumor suppressor genes can initiate skin cancers (basal cell carcinoma, squamous cell carcinoma, melanoma).
- Sunscreens contain chemical absorbers or physical blockers (e.g., zinc oxide, titanium dioxide) that prevent many UV photons from reaching the epidermis.
- DNA repair pathways and cellular checkpoints exist but are not activated or created by sunscreen; sunscreen’s role is preventive.

2) Step-by-step reasoning
- Step 1: Sunlight contains UV photons that reach skin. 
- Step 2: UV photons are absorbed by DNA bases, forming lesions (e.g., CPDs). 
- Step 3: If lesions are misrepaired or bypassed during replication, permanent mutations result. 
- Step 4: Repeated mutations increase cancer risk. 
- Step 5: Applying sunscreen lowers the flux of UV photons hitting skin cells, so fewer DNA lesions form, reducing the chance of mutation and lowering cancer risk.

3) Calculations/intermediate steps
- No numeric calculation is required here; the logical intermediate steps are the chain from reduced photon exposure → fewer DNA lesions → fewer mutations → lower cancer risk.

4) Why the correct answer is correct
- The correct option states that sunscreen reduces the chance of mutations caused by UV radiation. Because sunscreen blocks or absorbs UV, it prevents the initial DNA damage that leads to mutation-driven carcinogenesis, so it reduces cancer risk.

5) Why other options are incorrect
- "It doesn't; sunscreen causes mutation..." is false: sunscreens reduce UV exposure and thus reduce mutation risk; properly formulated sunscreens do not cause mutations.
- "Sunscreen can repair damaged DNA." Sunscreen is not a repair mechanism; cellular enzymes do that.
- "Sunscreen can activate checkpoints in skin cells." Checkpoints are cellular responses; sunscreen does not activate them.
- "Sunscreen can prevent cells with mutations from being destroyed." That would be harmful; sunscreen does not prevent apoptosis or immune clearance of mutated cells.

6) Conclusion
The correct answer is: "Sunscreen can reduce the chance of mutations caused by exposure to UV radiation present in sunlight." This explanation confirms and supports the provided answer.

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