Sneezing (also called sternutation) is a sudden, forceful, involuntary expulsion of air through the nose and mouth at speeds up to 100 mph (160 km/h), typically triggered by irritation or stimulation of the nasal mucosa. It serves as a protective reflex to clear the nasal passages of irritants, allergens, foreign particles, microbes, or excess mucus. Common causes include allergies (e.g., pollen, dust mites, pet dander leading to allergic rhinitis), viral infections (common cold or flu with nasal inflammation), irritants (strong odors, smoke, pollution, dry air, pepper, bright light—photic sneeze reflex in some people), sudden temperature changes, nasal tickling (e.g., from hair plucking or looking at sun), or hormonal shifts (e.g., pregnancy rhinitis). A typical sneeze sequence involves a deep inhalation, brief closure of the glottis, then explosive release with eyes often closing involuntarily; it may be single or in bursts, sometimes accompanied by a pre-sneeze tickle or “aah-choo” sound, watery eyes, nasal discharge, or mild headache from pressure changes.