When allergy season begins, many people wonder if the associated sneezing, congestion, and general malaise can cause a slight fever. Allergies often mimic the symptoms of a common cold, leading people to question if an elevated temperature signals an infection or an allergic reaction. Understanding the allergic response and the definition of a low-grade fever helps clarify why these symptoms might appear together.
Defining a Low-Grade Fever
A low-grade fever is a minor elevation in the body’s core temperature above the typical average of 98.6°F (37°C). When measured orally, this range is generally considered to be between 99.1°F and 100.4°F (37.3°C and 38.0°C).
A temperature above 100.4°F (38°C) is medically defined as a true fever, often signaling a significant immune response to an infection. While readings vary by measurement location, the 99.1°F to 100.4°F range serves as the benchmark for a minor elevation. This increase can be caused by various factors, including mild infections, inflammation, or certain medications.
The Allergic Response and Minor Temperature Elevation
An allergic reaction is an inflammatory response triggered by the immune system misidentifying a harmless substance as a threat. When exposed to an allergen, the body releases inflammatory mediators such as histamine and cytokines. These chemicals cause classic allergy symptoms, including sneezing, itching, and nasal congestion.
The release of these inflammatory compounds can affect the body’s thermoregulation, potentially leading to a subtle temperature increase. This systemic inflammation explains why some individuals report feeling warm or having a low-grade temperature during severe allergic episodes. However, the allergic response does not typically release pyrogens, the specific substances the body uses to intentionally raise temperature to fight infection.
Allergies can cause a slight temperature rise or make a person feel flushed, but they do not usually cause a true, sustained fever. If the temperature exceeds the low-grade range, the cause is likely a secondary issue. Prolonged inflammation and congestion from allergies can lead to a secondary infection, such as sinusitis, which then causes the true fever.
Differentiating Allergy-Related Symptoms from Infection
Distinguishing between allergies and an infection is important for appropriate treatment, especially when a low-grade temperature is present. Allergies are not contagious and often follow an exposure pattern, flaring up seasonally or after contact with a specific trigger like pet dander. Symptoms associated with an infection, such as severe body aches, fatigue, and a sustained fever, are usually absent or very mild with allergies.
The characteristics of nasal discharge and the presence of itchiness offer a key difference. Allergic rhinitis typically produces clear, thin, and watery discharge, often accompanied by intense itching of the eyes, nose, or throat. Conversely, a bacterial or viral infection often causes mucus that becomes thick, yellow, or green, and itchiness is not a primary symptom.
The duration and pattern of symptoms provide another clue. Allergy symptoms can persist for weeks or months, correlating directly with allergen exposure. Viral infection symptoms, like the common cold, usually run a defined course, improving within seven to ten days. A sporadic or very minor fever suggests an inflammatory process, while a sustained, higher temperature points toward a true infection.
When to Consult a Healthcare Provider
A low-grade temperature combined with allergy symptoms warrants professional evaluation if certain warning signs are present. Any temperature consistently above the low-grade threshold of 100.4°F (38°C) strongly suggests an underlying infection and should be reviewed by a healthcare provider. A fever lasting longer than 72 hours, even if low-grade, also requires medical attention.
Prompt consultation is needed if specific symptoms occur, including difficulty breathing, chest pain, or rapid worsening of symptoms. If typical allergy symptoms, such as congestion or sinus pressure, continue indefinitely or fail to improve after using over-the-counter medications, a doctor can determine if a complication has developed. Untreated allergic inflammation can lead to secondary conditions, such as a bacterial sinus or ear infection, which require targeted medical treatment.