What causes red line on skin while scratching?

Hello,

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From your brief history it looks like you are just having cholinergic urticaria which is nothing but a reaction that occurs with rise of body temperature. This is will also manifest as increased sweating. There is no need to panic as this subsides or gets better on its own with time. The main thing to do is avoid the triggering factor, like avoiding spicy and hot food, excising in an air conditioned or well ventilated room to a level where your body can tolerate the heat, avoiding hot showers, avoid over clothing yourself, do not wear tight clothes. You can take tablet Teczine M ( Montelukast+ Levocetrizine) once daily only in the night. It should be used only on the days you have irritation and not daily, and not for more than two to three weeks continuously. Use Calosoft lotion ( Calamine + Aloe vera) morning and night ( whenever you have the irritation). The red line appearing when you stroke your skin is because of the increased allergy level (IgE and ESR) in your blood which will increase on each flare up and reduce.