A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 23-year-old man comes to the emergency department because of a rash on his neck and back for the past 6 hours. He says that he first noticed some reddening of the skin on his back the previous evening, which turned into a blistering, red rash overnight. He went surfing the previous day and spent 5 hours at the beach. He reports having applied at least 1 oz of water-resistant SPF 30 sunscreen 30 minutes before leaving his home. His vitals are within normal limits. Physical examination shows erythema of the skin over the upper back and dorsum of the neck, with 3 vesicles filled with clear fluid. The affected area is edematous and tender to touch. Which of the following recommendations is most appropriate to prevent a recurrence of this patient's symptoms in the future?
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A
Reapply sunscreen after water exposureCorrect. water-resistant sunscreen loses protection after swimming; reapplication after water exposure is essential.
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B
Use SPF 50 sunscreenIncorrect. SPF 50 offers marginal extra protection (98% vs 97% UVB) and would not have prevented this sunburn without reapplication.
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C
Apply at least 3 oz of sunscreenIncorrect. 1 oz is the AAD-recommended full-body application; tripling is unnecessary and impractical.
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D
Use waterproof sunscreenIncorrect. The FDA prohibits 'waterproof' labeling on sunscreens — no sunscreen is waterproof; only water-resistant for 40-80 minutes.
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E
Wear a wide-brimmed hatIncorrect. A wide-brimmed hat adds physical UV protection but does not address the central failure here, which was lack of sunscreen reapplication after prolonged water exposure.
↑ Tap an answer to reveal the reasoning
Answer: A. A patient who used 1 oz of water-resistant SPF 30 sunscreen 30 minutes before sun exposure and surfed for 5 hours developed a severe sunburn with vesicles. The error is failing to reapply sunscreen after water exposure. 'Water-resistant' sunscreen, by FDA definition, maintains stated SPF for only 40 or 80 minutes of water immersion, after which protection diminishes significantly. The American Academy of Dermatology recommends reapplying sunscreen every 2 hours and immediately after swimming, sweating, or toweling off.
SPF 30 blocks about 97% of UVB radiation, which is adequate when applied properly. Going to SPF 50 yields only marginal additional protection (~98%) and is not the principal problem. The 1 oz amount used (a shot glass) is the AAD-recommended dose for full-body coverage; tripling that amount is unnecessary and not standard. The FDA discourages the term 'waterproof' as misleading — no sunscreen is truly waterproof.
The takeaway: even high-SPF sunscreen fails without reapplication, especially after swimming or sweating. Combine sunscreen with hats, UPF clothing, and shade for long sun exposure.
**Why each option:**
**A.** Correct — water-resistant sunscreen loses protection after swimming; reapplication after water exposure is essential.
**B.** SPF 50 offers marginal extra protection (98% vs 97% UVB) and would not have prevented this sunburn without reapplication.
**C.** 1 oz is the AAD-recommended full-body application; tripling is unnecessary and impractical.
**D.** The FDA prohibits 'waterproof' labeling on sunscreens — no sunscreen is waterproof; only water-resistant for 40-80 minutes.