Dr. Brian Orr talks about histamine and allergies in this  Interactive Health Clinic video.

What does histamine have to do with allergies?

During an allergic reaction, histamine makes blood vessels leaky so that cells from your immune system can migrate from the blood into the tissues to clear out the allergen. A side effect of this is that fluid leaks into the tissue and causes watery eyes, swelling in the nasal passages, and other allergy symptoms. Antihistamines block the receptors for histamine in the blood vessels, thereby putting a stop to most allergy symptoms.

Why do antihistamines make me sleepy?

Histamine has many functions in the body. In the brain, it’s a neurotransmitter and the brain cells that are most concerned with wakefulness are the ones that use histamine. By blocking the histamine receptors in the brain with antihistamines, we diminish wakefulness and get drowsy. And in sensory nerves histamine is a neurotransmitter for itchiness, which is why allergies and bug bites itch.

How can I take fewer antihistamines for my allergies?

Preventing the release of histamine in the first place is a good strategy for taking fewer antihistamines. You can do this with substances that stabilize the cells in the bloodstream that rip open to release histamine, like a group of compounds called bioflavonoids. Less histamine released in the bloodstream means fewer symptoms of allergies, and so there’s less need for antihistamines.