Macule
A reddish, flat lesion less than 0.5 cm in diameter is correctly termed a macule. 1
Dermatologic Terminology for Flat Lesions
The distinction between flat skin lesions is based primarily on size:
- Macule: A flat, non-palpable lesion less than or equal to 0.5 cm in diameter 1
- Patch: A flat, non-palpable lesion greater than 0.5 cm in diameter 1
This 0.5 cm cutoff represents the standardized international consensus for differentiating these two types of flat lesions. 1
Why the Other Options Are Incorrect
Papule: This describes a raised, palpable lesion less than 0.5 cm in diameter—the key distinguishing feature is elevation above the skin surface, not flatness 1
Plaque: This describes either a raised lesion or a flat lesion that is greater than 0.5 cm in diameter, making it too large to fit the question's criteria 1
Patch: While this is a flat lesion, it must be larger than 0.5 cm in diameter by definition, so it does not match the size criterion specified in the question 1
Clinical Context
The color (reddish) does not change the terminology—macules can be pigmented (brown, black), erythematous (red), or purpuric (purple). 2, 3 The defining characteristics for a macule are that it is flat (non-palpable), level with surrounding skin, and ≤0.5 cm in diameter. 1