Influenza (the flu) is a respiratory infection caused by the influenza virus, leading to symptoms like fever, body aches, cough, and fatigue. While a rash is not considered a typical symptom, its appearance is possible, though infrequent. Estimates suggest a rash occurs in a small percentage of cases, perhaps around 2% of those infected with influenza A. The presence of a rash can be confusing, as it may signal a direct effect of the virus or an entirely separate issue.
Viral Exanthem: The Direct Link
When the influenza virus itself causes a rash, it is categorized as a viral exanthem. This is a reaction of the immune system to a systemic viral infection. This type of rash is usually mild and often goes unnoticed, especially in adults, and appears to be more common in children.
The appearance is typically a faint, widespread pink or red rash composed of small, flat spots and slightly raised bumps, known as a maculopapular rash. This eruption generally does not cause intense itching and often begins on the trunk before spreading. The rash is a temporary manifestation of the body’s immune response and usually resolves on its own within a few days as the viral illness improves.
A maculopapular rash is not exclusive to the flu, as many common viruses can trigger a similar-looking skin reaction. The rash is a sign of the body actively fighting the infection. This direct viral exanthem often clears up within two to five days.
Rash Caused by Treatment or Secondary Infection
A rash appearing during or immediately after a flu episode may be caused by factors related to the illness or its treatment, rather than the influenza virus itself. Drug reactions are a frequent cause, especially if the patient is taking an antiviral medication like oseltamivir (Tamiflu). Oseltamivir can cause allergic reactions, including a skin rash, which necessitates stopping the medication and contacting a healthcare provider.
Rashes can also develop due to secondary infections that occur alongside or shortly after the flu, as the body’s immune system is temporarily weakened. For instance, a streptococcal infection (strep throat) can sometimes follow a viral illness and lead to scarlet fever. This bacterial infection causes a distinct rash that feels like sandpaper and is often concentrated in skin folds.
The use of antibiotics to treat a suspected or confirmed secondary bacterial infection can also be the source of a rash, often presenting as a delayed allergic reaction. Distinguishing between a primary viral exanthem, a drug reaction, or a secondary infection-related rash can be challenging. An evaluation by a medical professional is necessary to determine the exact cause of any new rash.
Urgent Signs: When to Seek Medical Attention
While many rashes associated with a flu-like illness are harmless, certain signs indicate a medical emergency requiring immediate attention. A rash that does not fade or blanch when pressed suggests bleeding under the skin. This non-blanching rash, known as petechiae (tiny spots) or purpura (larger spots), can be a sign of a severe condition like sepsis or meningitis.
Any rash accompanied by difficulty breathing, swelling of the face, lips, or throat, or blistering should be treated as a severe allergic reaction. This includes conditions like Stevens-Johnson syndrome, which is life-threatening. Other urgent signs include a high fever above 103°F combined with mental confusion, stiff neck, or extreme lethargy.
A rapidly spreading rash, especially one that is painful, or the appearance of blisters on the skin or mucous membranes should prompt an immediate trip to the emergency room. Seeking prompt medical evaluation for these urgent signs is the safest course of action to rule out serious complications. The presence of any unexplained rash in a child with a fever always warrants a medical assessment.