Antihistamines are commonly used to treat allergy symptoms, but one of the notable side effects they can induce is dry eyes. This occurs because antihistamines can diminish the production of tears and reduce moisture in the eyes. The active ingredients in antihistamines often work by blocking the action of histamine, which can lead to the drying out of mucous membranes, including those in the eyes. Dry eyes can manifest as discomfort, irritation, and a feeling of grittiness, which are particularly problematic for contact lens wearers. It's essential for individuals taking antihistamines to be aware of this side effect, particularly if they already suffer from dry eye syndrome or other ocular surface disorders, as it can exacerbate these conditions. In contrast, options like increased ocular pressure, redness of the eyes, and increased tear production are generally not associated with antihistamines. Increased ocular pressure is often linked to glaucoma therapy side effects, while redness of the eyes can stem from a variety of other conditions or irritants but is not a typical effect of antihistamines. Increased tear production would suggest an opposite reaction to what antihistamines typically cause, reinforcing that dry eyes is indeed the correct and relevant side effect related to eye health.