The exact cause is unknown, but it is associated with excessive exposure to wind, sunlight, or sand. Therefore, it is more likely to occur in populations that inhabit the areas near the equator, as well as windy locations. In addition, pterygia are twice as likely to occur in men than women.
Pterygium 
Maxilla
Dipygus
Periorbita
Tophus
Ipas 
Nasolabial fold
Oral torus