Dry mouth, medically known as xerostomia, occurs when the salivary glands do not produce enough saliva to keep the mouth moist. Saliva is important for oral health, as it neutralizes acids, washes away food particles, and prevents bacterial overgrowth. Allergies involve an immune system overreaction to a typically harmless substance, such as pollen, leading to symptoms like inflammation and congestion. The connection between allergies and dry mouth is driven by both the body’s physical response to allergens and the necessary treatments used to manage allergy symptoms.
The Physiological Link: How Allergies Affect Saliva Production
Allergies themselves do not directly cause the salivary glands to stop producing moisture. The primary physiological mechanism linking allergies to dry mouth is the nasal congestion resulting from the immune response. When nasal passages become inflamed and blocked due to allergic rhinitis, the body is often forced to switch from nasal breathing to oral respiration.
Breathing constantly through the mouth, particularly during sleep, leads to increased moisture evaporation from the oral tissues. This constant air movement across the tongue and mucous membranes dries out the mouth, creating the sensation of xerostomia. The underlying congestion is the indirect cause, as it triggers the mouth-breathing behavior.
Another factor is the mild dehydration that can accompany the body’s overall inflammatory response to an allergen. The immune system’s activity can contribute to subtle fluid loss, which in turn reduces the available moisture for saliva production. This combination of fluid loss and increased evaporation from mouth breathing provides a clear, non-medicinal pathway for allergies to lead to oral dryness.
The Pharmacological Link: Medications That Cause Xerostomia
The most common and direct cause of dry mouth among allergy sufferers is the medication used for treatment. Several classes of allergy drugs interfere with the nervous system signals responsible for saliva secretion. This side effect is known as an anticholinergic effect, which means the medication blocks acetylcholine, a neurotransmitter that stimulates salivary glands.
First-generation antihistamines, such as Diphenhydramine, have a high potential for causing dry mouth due to their strong anticholinergic properties. By blocking the signals that stimulate the salivary glands, these medications reduce saliva output. This drying effect is a frequent reason why patients often discontinue the use of these older drugs.
Decongestants, including active ingredients like Pseudoephedrine, also contribute to oral dryness through a different mechanism. These medications constrict blood vessels in the nasal passages to reduce swelling and mucus production. Because they dry up mucus in the sinuses, they can also reduce normal moisture production in the mouth as part of this generalized drying effect. Second-generation antihistamines, such as Loratadine or Cetirizine, are preferred because they have minimal anticholinergic properties and a lower risk of causing xerostomia.
Managing Dry Mouth While Treating Allergies
Managing dry mouth while treating allergies involves a combination of behavioral changes and specific remedies. Staying consistently hydrated by sipping water throughout the day helps counteract the drying effects of mouth breathing and medication. Avoiding beverages containing alcohol and caffeine is also advisable, as these substances can further exacerbate oral dryness.
Chewing sugar-free gum or sucking on sugar-free lozenges stimulates the salivary glands to produce more moisture. Using a humidifier, especially at night, adds moisture to the air and reduces the evaporative drying that occurs with nighttime mouth breathing. Practicing conscious nasal breathing during the day and using saline nasal rinses before sleep can help keep nasal passages clear, reducing the need for oral respiration.
If dry mouth persists despite these measures, over-the-counter saliva substitutes or moisturizing oral sprays can provide temporary relief. For those whose symptoms are linked to medication, discussing alternative treatments with a healthcare provider is a practical step. A doctor or pharmacist may suggest switching to a second-generation antihistamine or adjusting the dosage to mitigate the drying side effects.