Herpes zoster is still spreading after 3 days of medication, it may be a normal phenomenon, but also can be considered to be the use of medication is not right, the dose of medication is small and other factors related. 1. Normal phenomenon: herpes zoster is caused by varicella zoster virus infection, is an acute infectious skin disease. The disease is in the limit of proliferation period, even in the case of medication, may spread outward, is a normal phenomenon. 2. Incorrect medication: Herpes zoster is caused by a viral infection and is treated with antiviral drugs, such as acyclovir and valacyclovir, which can control the further reproduction of varicella-zoster virus. If the medication is not right, it may lead to spreading. 3. Small dosage of medication: It is recommended to use medication reasonably under the guidance of a doctor. If the dosage of medication is relatively small, it cannot play a role in controlling the virus and may lead to proliferation. Patients with shingles are advised to visit the dermatology department of the hospital in time and use the medication under the guidance of the doctor.