Antihistamines are common medications used to relieve symptoms of allergies, such as sneezing, itching, and runny nose. Many people wonder if taking these medications can lead to dehydration. While antihistamines do not cause systemic dehydration in the same way a lack of water does, some types can cause significant dryness in various parts of the body.
Impact on Body Moisture
Antihistamines do not cause overall body dehydration. Instead, they commonly cause a sensation of dryness in specific areas, particularly the mucous membranes. This effect is more pronounced with older, first-generation antihistamines like diphenhydramine (e.g., Benadryl) compared to newer, second-generation antihistamines such as loratadine (e.g., Claritin) or cetirizine (e.g., Zyrtec). First-generation antihistamines frequently cause dry mouth and dry eyes, while second-generation types are preferred for allergies due to fewer drying side effects.
Understanding the Drying Mechanism
The drying effect of certain antihistamines stems from their anticholinergic properties. Acetylcholine is a neurotransmitter that stimulates glands to produce secretions like saliva, tears, and mucus. Antihistamines with anticholinergic activity block the action of acetylcholine, particularly at muscarinic receptors in glands. This blocking action reduces secretions, leading to sensations of dryness.
First-generation antihistamines, such as diphenhydramine and chlorpheniramine, readily cross the blood-brain barrier and have stronger anticholinergic effects. This widespread action on acetylcholine receptors contributes to significant dryness. In contrast, second-generation antihistamines are more selective in their action, primarily targeting histamine H1 receptors in the periphery, with less ability to cross the blood-brain barrier or block acetylcholine receptors. This selectivity results in fewer anticholinergic side effects and less dryness.
Identifying and Alleviating Symptoms
The dryness caused by antihistamines can manifest in several ways. Common symptoms include dry mouth, also known as xerostomia, which can feel sticky or parched. Dry eyes, characterized by a scratchy or gritty sensation, and dry nasal passages, potentially leading to discomfort or nosebleeds, are also frequently reported. Some individuals may also notice dry skin.
Several steps can help manage these symptoms. Increasing water intake throughout the day can help alleviate dry mouth. Chewing sugar-free gum or sucking on sugar-free candies can stimulate saliva production, providing relief for dry mouth. For dry eyes, using lubricating eye drops (artificial tears) can keep the eyes moist. A humidifier in living spaces can add moisture to the air, helping with dry nasal passages and skin. Avoiding excessive caffeine and alcohol, which can contribute to dryness, can also be helpful.
When to Consult a Doctor
While dryness from antihistamines is often manageable, consult a healthcare professional if it is persistent, severe, or significantly impacts your daily quality of life. Symptoms such as blurred vision, difficulty urinating, or confusion, especially in older adults, warrant immediate medical attention as they can be signs of more pronounced anticholinergic effects. Seek guidance if dryness does not improve with self-care, if you have concerns about medication interactions, or if you have underlying health conditions affected by antihistamine use. Your doctor can assess your symptoms, consider alternative medications or dosages, or recommend specific treatments.