Autosomal Dominant Compelling Helioopthalmic Outburst (ACHOO) Syndrome is characterized by uncontrollable sneezing in response to the sudden exposure to bright light, typically intense sunlight. This type of sneezing is also known as photic sneezing. About one in four individuals who already have a prickling sensation in their nose will sneeze in response to sunlight, but “pure” photic sneezing is far less common. Sneezing is usually triggered by contact with infectious agents or after inhaling irritants, but the cause of photic sneezing is not fully understood. It may involve an over-excitability of the visual cortex in response to light, leading to a stronger activation of the secondary somatosensory areas. [from Medical Genetics Summaries]