Scarlet fever is not dangerous for most people when treated with antibiotics. It’s caused by the same group A strep bacteria behind strep throat, with the addition of a distinctive rash triggered by toxins the bacteria produce. Before antibiotics existed, scarlet fever killed thousands of children each year. Today, a standard course of antibiotics clears the infection reliably, and serious complications are uncommon. That said, untreated scarlet fever can lead to real problems, and recent outbreaks in several countries have put the disease back on the radar.
What Scarlet Fever Actually Is
Scarlet fever is essentially strep throat plus a rash. The bacteria responsible, group A streptococcus, produces powerful toxins that act as “superantigens,” meaning they trigger an unusually strong immune response. These toxins cause the hallmark signs: a red, sandpaper-textured rash that spreads across the body, a “strawberry tongue” that looks swollen and bumpy, and a high fever.
Interestingly, the rash isn’t caused directly by the toxins themselves. It’s actually a hypersensitivity reaction, meaning your immune system overreacts to the bacterial toxins based on previous exposure to strep. This is why the rash tends to appear in children who have had strep infections before and may be absent in those encountering the bacteria for the first time. The rash typically shows up 2 to 5 days after exposure and often concentrates in skin folds like the elbows, armpits, and groin, where it can form darker red lines.
Why It Used to Be So Deadly
In the 19th and early 20th centuries, scarlet fever was one of the leading causes of childhood death. Entire families could lose multiple children to a single outbreak. Without antibiotics, the infection could spread deeper into the body, causing abscesses, bloodstream infections, and organ damage. The development of penicillin in the 1940s transformed scarlet fever from a feared killer into a manageable childhood illness. The bacteria also appear to have become less virulent over time, though researchers don’t fully understand why.
Complications That Can Still Happen
When scarlet fever goes untreated or treatment is delayed, the infection can trigger complications that fall into two categories: those caused by the bacteria spreading directly, and those caused by the immune system misfiring afterward.
Direct complications include ear infections, sinus infections, and in rare cases, abscesses around the tonsils. Far more concerning are invasive infections where the bacteria enter the bloodstream or deeper tissues, potentially causing toxic shock syndrome. The same superantigen toxins responsible for the rash can, in severe cases, trigger massive inflammation that leads to dangerously low blood pressure and organ failure. This is rare but serious.
Immune-related complications can appear weeks after the initial infection, even if the sore throat seemed mild. Rheumatic fever, which can permanently damage heart valves, develops when the immune system attacks the body’s own tissues after fighting off strep. Post-streptococcal kidney inflammation is another delayed complication that causes swelling, dark urine, and high blood pressure. Both are preventable with timely antibiotic treatment.
The Link to Sudden Behavioral Changes in Children
A lesser-known complication involves the brain. PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections) is a condition where the immune response to strep bacteria mistakenly attacks parts of the brain, triggering a sudden, dramatic onset of obsessive-compulsive behaviors, tics, or severely restricted eating in children. Symptoms typically appear within three months of a strep infection, including scarlet fever, and can seem to come out of nowhere. A child who was previously fine may suddenly develop intense anxiety, repetitive behaviors, or uncontrollable movements. PANDAS is diagnosed in children between age 3 and puberty, and the key feature is that symptoms appear abruptly rather than gradually.
How It’s Treated
Antibiotics are the standard treatment, and they work well. Most children start feeling better within a day or two, and the rash gradually fades over the course of a week. The full course of antibiotics needs to be completed even after symptoms improve, because stopping early increases the risk of complications like rheumatic fever.
After at least 12 hours on antibiotics, the ability to spread the bacteria drops significantly. The CDC recommends that children stay home from school or daycare until they’ve been fever-free and on antibiotics for at least 12 hours, though 24 hours is recommended in certain situations like outbreaks or healthcare settings. The incubation period is 2 to 5 days, so if someone in your household is diagnosed, watch for symptoms in other family members during that window.
Recent Outbreaks Worth Knowing About
Scarlet fever hasn’t disappeared. Outbreaks re-emerged in China and several Asian countries starting around 2011, followed by the United Kingdom and other European countries around 2014. In 2022, multiple European countries reported surges in both scarlet fever and more serious invasive group A strep infections. Japan experienced a notable outbreak in the first half of 2024, with 656 reported cases of strep-associated toxic shock syndrome alone.
A 14-year surveillance study in Shanghai documented over 25,500 scarlet fever cases between 2011 and 2024. Incidence dropped during the COVID-19 pandemic, likely due to masking and social distancing, falling from about 17 cases per 100,000 people to roughly 5 per 100,000. But cases began climbing again as pandemic restrictions lifted, and new, potentially more virulent strains of the bacteria have been identified. These trends suggest scarlet fever cycles through periods of higher and lower activity, and we may be in a period of resurgence.
Who’s Most at Risk
Scarlet fever overwhelmingly affects children between 5 and 15 years old. Adults can get it, but it’s uncommon because most have built up immunity through repeated strep exposures over the years. Children in close-contact settings like schools and daycare centers are most likely to catch and spread the bacteria.
The people at greatest risk for serious outcomes are those who don’t receive antibiotics promptly, whether because symptoms are mild enough to be dismissed, access to healthcare is limited, or the diagnosis is missed. The rash is distinctive enough that most clinicians recognize it quickly, but in its early stages, scarlet fever can look like any other childhood fever with a sore throat. If you notice the telltale rough, sandpaper-like rash spreading across your child’s torso along with a fever and sore throat, that combination is the signal to get a strep test.