Fifth disease is a common viral infection caused by parvovirus B19, best known for producing a bright red rash on both cheeks that looks like the child has been slapped. It’s sometimes called “slapped cheek syndrome” or by its medical name, erythema infectiosum. The infection is usually mild in children and clears up on its own, but it can cause joint pain in adults and poses real risks during pregnancy.
The name “fifth disease” comes from an old numbering system for childhood rash illnesses. It was the fifth on a list that included measles, scarlet fever, rubella, and a couple of others. The name stuck even though nobody uses that list anymore.
What Causes It
Parvovirus B19 is a small DNA virus that spreads through respiratory droplets, the same way a cold does. Coughing, sneezing, and close contact are the main routes. It can also spread through blood, which is why it can pass from a pregnant person to their developing baby.
Once inside the body, the virus targets cells in the bone marrow that are responsible for producing red blood cells. It latches onto a specific receptor found on these cells and hijacks their machinery to make copies of itself. Because the virus can’t replicate on its own and depends on rapidly dividing cells, the bone marrow is its ideal environment. This temporarily slows down red blood cell production, which in healthy people causes little trouble but can be dangerous for anyone already dealing with a blood disorder.
How the Rash Develops
The illness typically starts with vague, cold-like symptoms: low-grade fever, headache, runny nose, and general fatigue. These appear about 4 to 14 days after exposure. A few days later, the signature bright red rash blooms across both cheeks. In children, this facial rash is often the first visible clue that something beyond a regular cold is happening.
Within a day or two of the facial rash, a second rash may spread to the chest, back, buttocks, arms, or legs. This body rash looks different from the cheeks. It has a lacy, net-like pattern and can be itchy. The whole rash typically fades within 7 to 10 days, but it can come and go for several weeks. Even after it clears completely, it sometimes reappears when the skin is exposed to sunlight, heat, cold, exercise, or rubbing.
Symptoms in Adults
Adults who catch parvovirus B19 often skip the dramatic facial rash entirely. Instead, the hallmark symptom is joint pain. About 60% of adolescents and adults with the infection develop some form of joint involvement, ranging from achiness to outright inflammatory arthritis. The hands are the most commonly affected area, particularly the small joints of the fingers, though knees, wrists, and ankles can also be involved. The pain is typically symmetrical, affecting both sides of the body at once.
For most adults, joint symptoms resolve within three weeks. However, roughly 20% of people experience lingering joint pain that can persist for months or, in rare cases, years. This can be frustrating because it may not be immediately obvious that a virus is the cause, especially if no rash appeared.
Why It Matters During Pregnancy
Fifth disease is generally harmless, but pregnancy is the major exception. About 30 to 33% of pregnant people who contract the virus pass it to the fetus through the placenta. The risk of serious complications depends heavily on timing.
Infection before 20 weeks of gestation carries the greatest danger. The period between 9 and 16 weeks is the highest-risk window. Because the virus attacks the cells that make red blood cells, a developing fetus can become severely anemic. This can lead to a condition called hydrops fetalis, where fluid accumulates abnormally in the baby’s tissues and organs. For infections in the first trimester, fetal loss can reach as high as 10%.
The risk drops significantly later in pregnancy. Fetal complications are rare during the last two months. Pregnant individuals who are exposed to someone with fifth disease can get a blood test to check their immunity status. Many adults were infected in childhood without realizing it and already carry lifelong antibodies that protect them.
Risks for People With Blood Disorders
Because parvovirus B19 temporarily shuts down red blood cell production, people who already have conditions like sickle cell disease or hereditary spherocytosis face a specific danger. Their bodies break down red blood cells faster than normal, so even a brief pause in production can trigger a steep drop in red blood cell counts. This is called a transient aplastic crisis, and it can cause severe, potentially life-threatening anemia that requires hospital treatment. In healthy children and adults, the temporary dip in red blood cell production goes unnoticed.
When You’re Actually Contagious
Here’s the tricky part: people with fifth disease are most contagious before any symptoms appear, during the early cold-like phase when they don’t know they have it. By the time the rash shows up, the infectious period is largely over. This makes it very difficult to prevent spread, since the most recognizable symptom arrives after the person has already been passing the virus to others.
Children with the rash don’t need to stay home from school or daycare on account of contagiousness. The horse has already left the barn, so to speak.
Diagnosis
In most children, diagnosis is straightforward. The slapped-cheek rash followed by a lacy body rash is distinctive enough that a doctor can identify it on sight. Blood tests aren’t usually needed for a typical case in a healthy child.
When testing is necessary, such as during pregnancy or in someone with a blood disorder, a blood test looks for two types of antibodies. One type (IgM) indicates a recent or current infection and becomes detectable about 10 to 12 days after exposure. Most people with the classic rash already have these antibodies by the time they see a doctor. The other type (IgG) shows up about two weeks after infection and remains in the blood for life, serving as a marker of past infection and ongoing immunity. If both antibody types are negative, the person has never been infected and has no protection.
Treatment and Recovery
There is no antiviral medication for parvovirus B19, and for the vast majority of people, none is needed. The infection runs its course on its own. Managing symptoms is the focus: rest, fluids, and over-the-counter pain relievers for fever or joint discomfort. Anti-itch creams or antihistamines can help if the body rash is bothersome.
People with weakened immune systems who can’t clear the virus on their own may need specialized treatment involving antibody infusions to help their body fight the infection. Those experiencing an aplastic crisis from an underlying blood disorder typically need blood transfusions to bridge the gap until red blood cell production resumes.
There is no vaccine for parvovirus B19. The most practical preventive measures are the basics: frequent handwashing, avoiding sharing utensils or cups, and covering coughs and sneezes. For pregnant individuals who work in settings with frequent outbreaks (schools, daycare centers), awareness of circulating cases and early testing after exposure are the best tools available.