Cold sores, also known as fever blisters and herpes labialis, are painful, fluid-filled blisters that usually develop on the borders of the lips and, sometimes, other places on the face or inside the mouth. Cold sores result from infection with one of two types of the herpes simplex virus. After the initial infection, the virus sequesters itself within nerve cells, where it can reactivate and cause recurrences. Topical or oral zinc supplements may help suppress cold sore recurrences and promote healing when outbreaks do occur.
In the August 2005 edition of the "Journal of Oral Pathology and Oral Medicine," oral surgeon Felice Femiano, DMD, explains that low levels of zinc cause a decline in the function of T-cells that normally fight cold sores. This can happen, Dr. Femiano says, "within a few days," of decreased blood levels of zinc. In a test tube, Dr. Femiano adds, zinc also counteracts the growth of the herpes simplex virus in the absence of T-cells, suggesting that zinc levels influence cold sore recurrences in more ways than one.
People can increase zinc levels through topical or oral zinc sulfate supplements. Zinc sulfate supplements for oral use are available without a prescription at most grocery and drug stores. However, topical zinc sulfate preparations must be prescribed by a doctor. Topical preparations that contain another form of zinc, zinc oxide, are readily available, but "probably ineffective," according to the University of Michigan Health System.
In the 2007 edition of "Integrative Medicine," University of Wisconsin professor David Rakel, MD, says that 25 mg of zinc sulfate with 250 mg of vitamin C taken by mouth every day can prevent cold sore outbreaks altogether in some people and reduce the duration of symptoms to one day in others. Topical preparations that contain 0.01% to 0.025% zinc sulfate produce similar effects. Zinc supplements typically cost less than prescription antiviral drugs and offer the additional benefit of being a more natural remedy.
Dr. Rakel warns that zinc competes with other nutrients—especially copper, calcium and iron—for absorption. People who take oral supplements in doses greater than 25 mg per day run the risk of becoming deficient in these other nutrients. For maximum effectiveness, people who also take iron or calcium supplements should take them separately from zinc supplements. Topical zinc preparations do not interfere with nutrient absorption, however they can cause skin irritation that prolongs the duration of cold sores and increases the risk of complications, such as secondary bacterial infections. These should be used only as directed by a physician.
Cold sore triggers vary from person to person and may include food allergies, sun exposure, stress, illness and nutritional factors other than zinc. Zinc supplements do not replace conventional medical treatments for cold sores. People who experience frequent or severe outbreaks or outbreaks that last longer than two weeks should seek advice from a doctor or dentist. As with any over-the-counter product, people who use zinc supplements should share this information with their health care providers.