Mouth Sores, Fevers and Blisters in Children

Sore in the mouth, fever and blisters either in or around the mouth or on other parts of the body can cause extreme discomfort and difficulty eating or drinking. If your child develops these symptoms, he may have one of several types of viruses, including Coxsackie virus, herpes simplex virus or chicken pox, caused by the varicella-zoster virus 1.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Coxsackie Virus

A child with mouth sores, blisters on other parts of the body and fever very likely has hand, foot and mouth disease, also known as Coxsackie virus 1. This disease is not related to hoof and mouth disease in animals. Coxsackie virus, a contagious disorder that can cause your child extreme misery, most often affects children between the ages of 6 months and 3 years, according to the Ask Dr. Sears website 1. Fever and malaise along with painful mouth blisters may start a day before the blisters and rash appear in other areas, mostly on the palms of the hands and soles of the feet as well as the diaper area.

Herpes Simplex-2 Virus

Your child could also have a herpes simplex viral infection, also known as a cold sore or fever blister. In a herpes simplex infection, blisters do not occur on other parts of the body. Herpes simplex virus can cause mouth sores that occur only around the lips, although they can also develop inside the mouth. Fever can also occur with a herpes infection, especially when the child has his first outbreak. Subsequent infections don't usually cause fever. Around 62 percent of Americans have been exposed to the herpes simplex virus by adolescence, according to dentist Daniel Ravel on his website, Pediatric Dental Health 4.

Chicken Pox

Chicken pox is a common childhood illness unless your child has been vaccinated against the disease. A child with chicken pox usually has quite a few more blisters than a child with Coxsackie virus or herpes simplex 1. Blisters can occur on any part of the body, including inside the mouth. The blisters of chicken pox cause considerable itching. Fever, sore throat and feeling unwell often occur a day or two before the child breaks out in reddish bumps that blister, break and scab over a several day period. New crops of bumps break out over a two to four day period. Very high fever, cough, mental changes, confusion or extreme drowsiness can indicate serious complications and require medical evaluation, reports KidsHealth from Nemours Foundation.


Most diseases that cause mouth sores, blisters and fever are caused by viruses and resolve on their own within a short time. While it's always good to notify you doctor when your child has an illness, these illnesses generally don't require medical treatment. However, continuing or very high fever, headache, mental changes or stiff neck do need evaluation. Call your child's doctor if these symptoms occur.