Smelling salts contain ammonia-based chemicals that, when inhaled, irritate the nose and throat, triggering a reflex that increases breathing rate and heart rate. This sudden irritation causes the person to take a deep breath, increasing oxygen intake to the brain and temporarily increasing alertness and wakefulness. The effects of smelling salts include:

• Temporary increase in heart rate
• Irritation of the nasal and respiratory membranes
• Increased oxygen delivery to the brain
• Activation of the body's "fight-or-flight" stress response, which can make someone feel more alert or energized

They are commonly used to revive people who have fainted or become lightheaded, and some athletes use them to boost focus temporarily. However, they do not increase muscle strength and are not proven to enhance athletic performance. On the downside, smelling salts can cause irritation or chemical burns in the nose, eyes, skin, and lungs if overused or held too close. They can worsen respiratory conditions like asthma and bronchitis and may cause allergic reactions in some people. Additionally, the reflex triggered by smelling salts can cause a sudden head jerk, which could be harmful if a person has a neck or spine injury. In summary, smelling salts cause a sharp irritation that triggers increased breathing and heart rate to temporarily boost alertness, but there are potential risks with misuse or overuse.