Which type of radiation produces a homogenous erythema?

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

Answer: (B)

Ultraviolet radiation tends to produce a uniform reddening across the area that has been exposed because the skin’s inflammatory response is triggered evenly where the UV dose is the same. The redness comes from vasodilation and increased blood flow as the skin reacts to DNA disruption and inflammatory mediators released in the exposed epidermis. When the exposure is uniform, this response is also uniform, leading to a homogenous erythema across the treated skin.

Infrared radiation, on the other hand, is primarily a heat source and can cause thermal injuries that may vary with tissue depth, moisture, and cooling, so the resulting redness is not necessarily uniform. The terms minimal erythema and second-degree erythema describe levels or severity of erythema after exposure, not the type of radiation causing it, so they aren’t about the source of the redness itself.