What Is Sixth Disease?

Sixth disease, also known as roseola, is a very common illness in children. Learn more about the symptoms, causes, and treatment.

Medically reviewed by Teja Dyamenahalli, MD, MPH, FAAP

If there's one thing that's true about kids, it's that they will get sick from time to time, whether it's a cold, the flu, rashes, and more. One of the most common causes of illness in older babies and toddlers is sixth disease, more commonly known as roseola.

Roseola, or sixth disease, is a virus caused by human herpes virus 6 (HHV-6) and is most common in babies and toddlers between 6 months and 2 years old. “Moms pass antibodies to the baby during pregnancy, which is why infections are not as common in the earlier life—the baby has the antibodies,” explains pediatrician Edmund Milder, MD, an infectious diseases specialist at Rady Children’s Hospital – San Diego. “As the maternal antibodies wear off, they become susceptible and will get infected in the 6 months to 2 years range.”

Ahead, find out more about roseola, including the symptoms, diagnosis, treatment, and when to contact a health care provider for more help.

Related: The Most Common Skin Rashes in Children and Their Causes

How Common Is Sixth Disease?

Roseola is extremely common in young children. “Almost everybody has had an infection by the time they are 2 or 3 years old,” says Dr. Milder. “And once you’re infected, you keep it forever. It goes into a latent state where it’s not bothering you clinically and sort of hangs out.” This is common with all the herpes viruses—herpes simplex, for example, stays dormant in the body until it is activated, at which point it causes a cold sore. But with HHV-6, you don’t have to worry about it reactivating and making you sick again. “It is able to be found in saliva when it reactivates, but it doesn’t cause disease,” Dr. Milder adds.

Roseola is so common in this age group that research suggests it is responsible for up to 45% of fevers in infants (though not all of them will be diagnosed with roseola; more on that below). “While there are estimated over three million cases a year, it does not tend to have the large 'outbreaks' like we usually tend to see with flu,” adds Sandra McKay, MD, a pediatrician with UTHealth Houston.

Symptoms of Sixth Disease

A classic presentation of roseola includes three to five days of a very high fever, which can reach up to 104 degrees, after which, the child may get a red, bumpy rash over their body. Dr. Milder points out that about 20% of kids will have this classic presentation of the disease, adding, "The rash looks dramatic but they are feeling fine, that’s actually the end of them feeling sick."

For the remaining 80% of children, roseola can look like any other childhood illness, causing issues like a runny nose, GI symptoms, malaise, conjunctivitis, a decrease in appetite, cough, or a fever with no rash.

The most common complication of roseola is a febrile seizure—a seizure in a child that’s caused by a fever. Up to 15% of children with roseola may experience a febrile seizure, but these typically only last a few minutes and are usually harmless. However, if you suspect your child is experiencing a seizure, be sure to reach out to a health care provider or seek medical care immediately.

How Is Sixth Disease Diagnosed?

Because roseola is hard to identify without the presence of a rash, the virus often goes undiagnosed and is typically treated like any other childhood illness. “A diagnosis is typically made once the rash presents, and that happens usually after the fever breaks,” adds Dr. McKay. “It is hard to make the diagnosis of roseola before the rash.”

How Is Sixth Disease Treated?

Since roseola is a viral infection and not a bacterial infection, there aren't prescription antibiotics for this illness. Instead, you’ll want to manage your child’s symptoms to keep them comfortable. That means lots of rest, making sure they are remain hydrated, and using children's Tylenol to control their fever.

Related: Can You Alternate Between Tylenol and Ibuprofen When Your Child Is Sick?

Is Sixth Disease Contagious?

While roseola is technically contagious, the chances that your child got it from someone else who was sick with the same virus are low. “Because we all keep [the virus] and shed it frequently, the opportunity to get it from someone who isn’t sick is more likely,” says Dr. Milder. “Most people get it from a healthy person.” Indeed, Dr. Milder adds that 60-70% of healthy adults will have the HHV-6 virus present in their saliva at any given time, so there’s a better chance of your child getting it from a healthy adult than from another sick toddler.

When to Contact a Health Care Provider About Sixth Disease

While roseola is very common and most children recover just fine, it's important to reach out to a health care provider if:

• Your child is less than 3 months old and has a temperature of 100.4°F or higher

• Your child is between 3 to 6 months with a fever of 102°F or higher

• Your child is older than 6 months with a fever of 103°F or higher

• Your child looks extremely ill, seems exceptionally drowsy, or fussy

• They've had a seizure

• They have any other severe symptoms like a stiff neck, unexplained rash, extreme sore throat and/or ear pain, repeated vomiting or diarrhea

“In general, a fever for 48 hours without any other symptoms is worth getting checked out by a health care provider,” adds Dr. Milder. With roseola, either the fever will go away, or other symptoms will present after a few days that might reveal to a doctor the cause of the fever.

“One thing I like to stress is that while fever can make you feel bad, it’s actually good for you,” says Dr. Milder. “Our immune systems work better at higher temperatures; you tip the balance towards beating the infection when you have a fever. A fever is a healthy response to a disease.”

Related: What Does Heat Rash Look Like in Kids?

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