Infections are one of the most common causes of hives, especially in children, where they account for more than 40% of acute cases. Viral, bacterial, and parasitic infections can all trigger the itchy, raised welts that characterize urticaria. The connection often surprises people who assume hives are always an allergic reaction to food or medication, but your immune system’s response to fighting an infection can produce the exact same skin reaction.
How Infections Trigger Hives
Hives appear when certain immune cells in your skin release histamine and other inflammatory chemicals. This is the same process behind allergic hives, but the trigger is different. Instead of reacting to an allergen, your immune system is responding to a pathogen, and the skin gets caught in the crossfire.
There are several ways this can happen. The infection may activate your complement system, a cascade of proteins that amplifies immune responses and can destabilize mast cells in the skin. Circulating immune complexes (clusters of antibodies bound to parts of the pathogen) can also deposit in skin tissue and provoke inflammation. In some cases, the pathogen’s own toxins or structural components directly trigger mast cells to release histamine. A more indirect route involves molecular mimicry, where parts of the pathogen resemble your own tissue closely enough that the immune response spills over into attacking the body itself. This can set off a form of autoimmune-driven hives that persists even after the original infection clears.
Viral Infections
Viruses are the single most common infectious trigger for hives, particularly in children. Upper respiratory infections, including the common cold and flu, frequently cause hives that appear during or just after the illness. Many parents notice their child breaking out in welts while fighting a fever or runny nose, and the viral infection itself is typically the cause rather than any medication being given.
Specific viruses linked to hives include Epstein-Barr virus (the cause of mono), hepatitis A, B, and C, cytomegalovirus, and various respiratory viruses. COVID-19 has also been associated with urticaria in some patients. In many cases, particularly with common colds, the specific virus is never identified because the hives resolve on their own as the infection clears. The rash typically appears within days of the first symptoms of illness and can last anywhere from a few days to several weeks.
Bacterial Infections
A wide range of bacterial infections have been linked to hives. The most commonly cited include Helicobacter pylori (a stomach bacterium), Streptococcus (strep throat), Staphylococcus, Mycoplasma pneumoniae (a cause of walking pneumonia), Salmonella, Borrelia (the bacterium behind Lyme disease), and Yersinia enterocolitica (a foodborne pathogen). Less common associations include Brucella, Chlamydia pneumoniae, and even Mycobacterium leprae.
The hives can result from the bacteria being present in the skin, from toxins the bacteria release into the bloodstream, or from immune complexes formed as the body fights the infection. In some of these cases, treating the underlying bacterial infection resolves the hives entirely.
The H. Pylori Connection
H. pylori deserves special attention because it’s one of the most studied bacterial links to chronic hives, the kind that persist for six weeks or longer. A meta-analysis found that H. pylori infection is significantly more common in people with chronic hives than in the general population, with about 66% higher odds of having the infection. One study found that 80% of chronic hives patients who tested positive for H. pylori experienced complete remission of their skin symptoms after the infection was treated with antibiotics.
That said, the evidence is mixed. Other reviews using stricter criteria found the benefit of treating H. pylori for hives to be weak and inconsistent. The association is real but modest, and not every case of chronic hives linked to H. pylori will clear up with treatment. Still, testing for H. pylori is worth considering if you have chronic hives with no obvious cause, especially if you also have digestive symptoms like stomach pain or acid reflux.
Parasitic Infections
Parasites are a less common but well-documented cause of hives, particularly in regions where parasitic infections are more prevalent. The list of parasites associated with urticaria is long: roundworm, Toxocara (from dog or cat roundworm), Giardia, Strongyloides, Trichinella, Schistosoma, tapeworm (hydatid disease), liver fluke, Anisakis (from raw fish), Blastocystis, and filarial worms.
Parasitic hives tend to be chronic and persistent. French studies found a high prevalence of Toxocara markers in patients with chronic urticaria, though anti-parasitic treatment didn’t consistently resolve the hives. With Giardia, the skin symptoms are thought to be secondary to the gut infection, and they often disappear once the parasite is treated. If you have unexplained chronic hives along with gastrointestinal symptoms, travel history to tropical regions, or exposure to contaminated water, a parasitic cause is worth investigating through stool testing or blood work for specific antibodies.
Infection Hives vs. Allergic Hives
The welts themselves look identical regardless of cause. Individual hives typically fade within 30 minutes to 24 hours, with new ones appearing as old ones resolve. The key differences are in timing and context.
Allergic hives usually appear within one to two hours of exposure to a specific trigger, such as a food, medication, or insect sting. They tend to resolve quickly once the trigger is removed, often within hours to a few days. Infection-related hives, by contrast, develop alongside illness symptoms like fever, sore throat, cough, or stomach upset. They may persist for days to weeks, tracking with the course of the infection rather than a single exposure event. Acute urticaria is defined as lasting up to six weeks. When hives continue beyond that threshold, they’re classified as chronic, and hidden infections like H. pylori or parasites become more relevant possibilities.
Another clue is that infection-related hives often don’t respond as cleanly to antihistamines. They may improve somewhat, but the hives keep recurring until the underlying infection resolves. If you’re taking antihistamines for hives and they keep coming back over days or weeks, especially alongside other symptoms of illness, the cause is more likely infectious than allergic.
Why This Matters for Children
In children, infections are the leading cause of acute hives, responsible for more than 40% of cases. Kids get frequent viral infections, and their immune systems tend to mount robust, sometimes exaggerated inflammatory responses. A child who breaks out in hives during a cold or stomach bug is experiencing a very common reaction. The hives in these cases almost always resolve on their own once the virus runs its course, typically within a few days to two weeks. Repeated episodes of hives in a child who gets frequent colds are more likely to be infection-driven than allergic, even though the instinct is often to search for a food allergy.
How Infection-Related Hives Are Identified
There’s no single test that confirms hives are caused by an infection. The diagnosis is usually made by putting together the clinical picture: hives appearing alongside signs of illness, no clear allergic trigger, and resolution of hives as the infection clears. For acute viral hives, no workup beyond a basic exam is typically needed.
For chronic hives lasting more than six weeks, the search becomes more targeted. Testing may include blood work for markers of infection and inflammation, H. pylori breath testing or stool antigen testing, stool samples for parasites, and sometimes blood tests for specific antibodies to parasites like Toxocara. Dental infections, sinus infections, and urinary tract infections are also checked as potential hidden sources. When the infection is found and successfully treated, the hives often resolve, sometimes confirming the connection only in hindsight.