Red marks appear on the leg after scratching.

Red marks appearing after scratching the legs are usually a normal phenomenon, but they may also be caused by conditions such as allergic dermatitis or dermographism (artificial urticaria). Patients should address the issue according to the specific underlying cause. Detailed analysis is as follows:

1. Physiological Factors

If the legs are scratched vigorously, minor damage to superficial capillaries in the skin may occur, resulting in red marks. This is considered normal and typically resolves on its own without concern.

2. Disease-Related Factors

1) Allergic Dermatitis
This is often related to recent exposure to allergens. Patients with allergic dermatitis may experience localized skin warmth and itching; scratching can lead to visible marks on the skin surface. Under medical guidance, patients should apply topical medications such as calamine lotion or hydrocortisone butyrate cream to relieve symptoms.

2) Artificial Urticaria (Dermographism)
Artificial urticaria is a skin allergic reaction that occurs after scratching or trauma to the skin, characterized by raised, red, linear lesions accompanied by itching. Patients may follow medical advice to apply topical compound acetic acid dexamethasone cream or take oral antihistamines such as chlorpheniramine maleate tablets for treatment.

In addition to the common causes mentioned above, other possible factors include contact dermatitis, neurodermatitis, allergic purpura, and urticarial vasculitis. Patients should maintain proper skin care and avoid excessive scratching of affected areas.