How long does antiviral treatment take to work for cold sores?

Cold sores, also called herpes labialis, often begin with tingling or burning before blisters appear. Antiviral medicine works by slowing the virus's ability to multiply. Starting it during the early tingling stage may give it the best chance to shorten or soften the episode. Improvement may show as less new blistering, reduced discomfort, and gradual drying rather than an instant change. A crust can remain after the active virus is settling, so skin appearance may lag behind symptom relief.

Take or apply the medicine exactly as prescribed and complete the recommended course unless the prescriber changes it. Keep the area clean, avoid picking the crust, and wash your hands after touching it. Do not share lip products, towels, or utensils while a blister is present, and avoid kissing or oral contact because the virus can spread even when the sore seems to be improving. A pharmacist or clinician can advise on pain relief and whether your medicine is suitable with other treatments.

Arrange medical advice if sores are frequent, unusually severe, spreading, or not beginning to improve as expected. Seek urgent care for eye pain, a red eye, vision changes, severe headache, confusion, marked weakness, or difficulty drinking. People with a weakened immune system, extensive eczema, or a newborn in close contact should seek advice promptly because herpes infections can be more serious in these settings.

Ask whether your medicine should be started at the first tingling, how long to use it, and what to do if a dose is missed. Ask which symptoms would suggest eye involvement or a different diagnosis, and whether recurring episodes warrant a prevention plan.