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Itching on the stretch marks is quite common and can be due to dryness,allergy or any infection.Avoid using any harsh soaps and apply Aloe Vera gel on those marks.It will relieve itcing and give soothing effect.After bath apply Calamine lotion on it.Wear loose cotton clothes.
If the itching persists kindly see a Physician for evaluation.You might require some antihistamine medications for treatment.
Take Care!