In ultraviolet radiation dosage guidelines, which statement is correct?

• A. The erythemal response of the patient guides dosage
• B. There is no standard distance used for placement
• C. A dose causing erythema can be used immediately after a previous exposure has subsided
• D. All of the above

Answer: (A)

The key idea is that UV dosage is tailored to how an individual’s skin responds to radiation, using the minimal erythemal dose (MED) as the anchor. By determining MED, clinicians set therapeutic doses at or below the level that produces the slightest redness, and adjust over time as the skin's response changes. This patient-specific approach makes the erythemal response the best guide for dosage. It's not correct to say there’s no standard distance for placement—device guidelines provide recommended distances, so this statement isn’t accurate. It’s also unsafe to re-dose to provoke erythema immediately after a previous exposure; guidelines typically require waiting for any redness to subside or using a lower, non-erythemal dose. Therefore, guiding dosage by the erythemal response is the correct concept.