Fever blisters are fairly common and are also often called cold sores, but have nothing to do with a cold. These sores typically appear on the outside of the mouth, on the lips. The majority (about 95%) of fever blisters are due to a virus, typically herpes type 1. Because the fever blister is due to a virus they are contagious and most people will be exposed to the virus during their lifetime. Children are typically exposed via contact from an adult, a sibling or a relative who has a fever blister, or by other children who have mouthed toys etc that may have been contaminated with the virus. In many cases the exposure may be asymptomatic while others will develop painful vesicles appearing both inside the mouth, on the tongue and gums, as well as on the lips about 3 -5 days after their exposure. This initial illness is called herpetic gingivostomatitis. The initial infection tends to be more uncomfortable and may take up to two weeks for the lesions to resolve. The most difficult problem is due to oral discomfort so it is important to make sure that these young children stay hydrated. Popsicles are often helpful for this. Once you have been exposed to the herpes virus the virus remains in nerve endings where it may be dormant and asymptomatic for years. About 60% of children are positive for HSV -1 by adolescence. At other times the virus may become active (times of stress, sun exposure, fever, menstrual periods) and result in a fever blister. If a child develops a fever blister, they too are contagious and may spread the virus to others by touching or picking at the lesion and then touching other people or objects with their mouths. Fever blisters may be treated in most cases by using a topical antiviral that may be applied to the lesion. These are prescription medications that may shorten the duration of the fever blister by a day or two, especially if started early and applied frequently. If children experience recurrent fever blisters speak with your pediatrician about the use of oral antiviral medications. Remember, if you have a fever blister don't kiss your baby. Although the most viral shedding occurs after the initial HSV infection, you remain contagious with each fever blister so it is better to take precautions for a few days. That's your daily dose for today. We'll chat again tomorrow.