Allergy symptoms, such as sneezing, congestion, and itchy eyes, arise from an immune system overreaction to a typically harmless substance, like pollen or pet dander. This response involves the body releasing inflammatory chemicals, primarily histamine, which causes the familiar symptoms. Symptoms are rarely constant, often appearing, worsening, and then disappearing unpredictably. This fluctuation occurs because the body’s sensitivity and the level of exposure to allergens are constantly changing based on external and internal factors.
The Influence of Environmental Cycles and Allergen Load
The amount of allergen a person encounters is the most common reason for symptoms coming and going. Pollen counts fluctuate significantly throughout the day, driven largely by weather patterns. Levels typically rise in the morning, peaking around midday or early afternoon when temperatures are warmest and humidity is low.
Windy and dry conditions can stir up and spread pollen over long distances, leading to higher airborne concentrations. Conversely, rain often provides a temporary reprieve by washing pollen out of the air, causing levels to drop dramatically. This relief can be short-lived, as rain also encourages the growth of mold, another common allergen, which can lead to later symptom flare-ups.
A change in location can alter the total allergen load and symptom severity. Moving indoors may reduce exposure to outdoor pollens but increase contact with perennial allergens like dust mites and pet dander. Symptoms may worsen at night or in the early morning if a person is exposed to high concentrations of dust mites in their bedding. This continuous shift means the immune system is processing a varying amount of irritating particles.
Internal Factors Modifying Immune Response
Even when allergen exposure remains steady, the body’s internal state can modify its sensitivity, making symptoms appear or subside. One significant factor is the body’s stress response, mediated by the hormone cortisol. While cortisol is a natural anti-inflammatory that can suppress immune reactions short-term, prolonged or chronic stress can disrupt this balance.
Sustained high stress levels can lead to immune dysregulation, making the body hyper-responsive and lowering the threshold for an allergic reaction. This heightened inflammation means the immune system reacts more severely to a standard dose of allergen. Fighting off a cold or viral infection can also temporarily heighten overall immune reactivity, causing allergy symptoms to feel worse than usual.
The concept of an “allergy threshold” helps explain this intermittent sensitivity. Symptoms only become noticeable when the total burden on the immune system—including exposure to multiple allergens, current illness, and internal stress—exceeds an individual’s specific limit. This cumulative exposure means a person might tolerate a certain amount of pollen, but adding the inflammatory load from a stressful day tips them into a full allergic reaction.
Hormonal fluctuations, such as those associated with the menstrual cycle or pregnancy, can also impact blood flow and swelling in the nasal tissues. This temporary change can increase congestion and sensitivity.
Understanding the Rebound Effect
Symptoms that appear suddenly and intensely, particularly congestion, may be a consequence of treatment rather than a true allergy flare-up. The most common pharmacological cause is rhinitis medicamentosa, also known as rebound congestion. This condition is triggered by the overuse of topical decongestant nasal sprays containing vasoconstrictors like oxymetazoline. These sprays narrow blood vessels in the nasal lining, rapidly reducing swelling. If used for more than the recommended period (typically three to seven days), the nasal tissues become dependent on the medication.
When the medication wears off, the blood vessels over-compensate by swelling dramatically. This creates a cycle of worsening congestion that drives the user to spray again, mistakenly believing their allergies are worsening.
A natural physiological mechanism called the nasal cycle can also make congestion feel intermittent. The turbinates, structures inside the nose that regulate airflow, naturally swell and shrink cyclically, shifting airflow from one nostril to the other every few hours. While usually unnoticeable, this normal swelling can feel like congestion is coming and going, especially if the nasal passages are already slightly inflamed.