Achoo syndrome is a condition marked by almost uncontrollable bouts of sneezing triggered reflexively when someone accustomed to darkness suddenly encounters bright light, typically from sunlight. Individuals may sneeze 2 or 3 times in a row, but episodes can extend to around 40 sneezes. This condition is also known as the photic sneeze reflex or helio-outburst syndrome. The syndrome is more prevalent than often assumed. A study revealed that 23% of medical students experienced it. This is one of the most common genetic traits and is inherited in a way that equally affects both males and females. Those with the condition have a 50% chance of passing the Achoo gene to each child, who will then also have the syndrome. For sufferers, moving from tunnels or shaded areas created by tall buildings or dense forests into bright sunlight can trigger sneezing.