Ultraviolet radiation–induced erythema is intense after how many hours?

• A. Infrared radiation
• B. Minimal erythema
• C. Ultraviolet radiation
• D. Second-degree erythema

Answer: (C)

The key idea is that redness from UV exposure is a delayed inflammatory response. After ultraviolet radiation hits the skin, erythema doesn’t appear immediately; it typically shows up within several hours and reaches its maximum intensity about a day or two after exposure, often peaking around 24 to 48 hours. This timing reflects the cascade of inflammatory mediators released in response to UV-induced skin cell damage.

So, ultraviolet radiation is the trigger for this erythema—the cause of the reaction you’re studying. Infrared radiation would produce heat-related effects rather than the classic UV-induced erythema. The term minimal erythema refers to the smallest UV dose that produces redness after about 8–24 hours, not the timing of the intense erythema itself. Second-degree erythema isn’t a standard way to describe UV-induced redness; it implies a deeper burn rather than the typical sunburn pattern.

Understanding this timing helps explain why the erythema is described as intense after a delay rather than immediately.