Antihistamines: What They Do and When to Use Them

If your nose itches, eyes water, or hives pop up, antihistamines are often the fastest way to feel better. They block histamine, a chemical your body makes during allergic reactions. That reduces sneezing, itching, runny nose, and some skin reactions.

Types and common drugs

Antihistamines come in two groups: first‑generation (sedating) and second‑generation (non‑sedating). First‑generation examples include diphenhydramine (Benadryl), chlorpheniramine, and promethazine. These work fast but often cause drowsiness and dry mouth.

Second‑generation options cause less sleepiness and are better for daily use: loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra). Many people use them for seasonal allergies, chronic allergic rhinitis, and long‑term management of hives.

How to choose and use them

Want daytime relief without fogginess? Start with a second‑generation antihistamine. Need something for a single night of severe itching or to help sleep after intense allergy symptoms? A single dose of a first‑generation drug can help, but don’t drive afterward.

Read labels carefully. Over‑the‑counter allergy pills show dosing by age. Don’t combine oral antihistamines with multi‑symptom cold meds that already contain one — you can double up by mistake. For congestion, nasal steroid sprays are usually more effective than oral antihistamines.

Some antihistamines come as nasal sprays or eye drops. Nasal antihistamine sprays work faster for runny nose and sneezing, while eye drops target itchy, red eyes directly. Choose the form that treats your main symptom.

Safety tips and interactions

Avoid alcohol and other sedatives if you take a sedating antihistamine — mixing increases drowsiness and slows reactions. Older adults should be wary of first‑generation drugs; they raise the risk of confusion, falls, and urinary problems because of anticholinergic effects.

Kids need age‑appropriate doses. Do not give adult tablets to young children. For infants and toddlers, check with your pediatrician before using any antihistamine. Pregnant or breastfeeding people should ask their provider which option is safest.

If you take other medicines (antidepressants, sleep aids, blood pressure drugs), tell your prescriber before starting an antihistamine. Some interactions can increase side effects or reduce effectiveness.

If allergies don’t improve after a week or two of OTC meds, or if you have severe symptoms like trouble breathing or facial swelling, seek medical care right away. For chronic problems, an allergy specialist can run tests and suggest targeted treatments like immunotherapy.

Small steps make a big difference: pick a non‑sedating pill for daytime, check labels for dosing, avoid mixing meds, and talk to your clinician about long‑term options. Antihistamines help a lot when used the right way.