This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Dermatitis Erythema, Subject name: Skin
"White dermographism" is seen in? 
Select and explain. 
A. Atopic dermatitis, B. Airborne contact dermatitis, C. Chemical dermatitis, D. Seborrheic dermatitis
A: Atopic dermatitis
Answer: A: Atopic dermatitis 
Explanation: Ans. A. Atopic dermatitisWhite dermographism is seen in atopic dermatitis due to capillary vasoconstriction following light stroking of the skin.The small blood vessels in atopic dermatitis show a tendency to vasoconstriction responses.1. Pallor of the skin after stroking (white dermographism)2. Delayed blanch with acetylcholine3. White reaction to nicotinic acid esters4. Abnormal reactions to histamine in affected skin5. Low finger temperature6. Pronounced vasoconstriction on exposure to cold.None of these findings is pathognomonic.