Increased activity at Popocatepetl, Mexico’s largest volcano, has led to flight disruption and the closure of some schools in the area. The National Centre for Prevention of Disasters (CENAPRED) on 21 May raised the alert level to yellow phase three, meaning people living nearby should prepare for possible evacuation. International SOS's security specialist Paulina Bouchot and Medical Director, Dr Albert Castano assess the security implications and offer medical advice.