Laughter is simply the physiological response to humor. Laughing makes us feel good for a reason. The physiological effects on our body do some pretty amazing stunts. Laughter boosts the Immune System. It also increases the concentration of salivary immunoglobulin A, which defends against the entry of infectious organisms through the respiratory tract.
Laughter basically brings balance to all the components of the immune system.
Blood Pressure is lowered, and there is an increase in vascular blood flow, and an increase in oxygenation of the blood, which further assists healing. Laughter may lead to hiccupping and coughing, which will clear the respiratory tract by dislodging mucus plugs. Laughter also gives your diaphragm and abdominal, respiratory and facial, leg and back muscles a workout. So basically laughter is an all over body workout. There also has been some belief that laughter may help prevent some life-threatening diseases such as heart disease.