The 8-hour shift work is one of the main achievements of the organized workers. International solidarity with United States miners, who were massacred in Chicago in 1886, and the aftermath of World War I promoted the establishment of 8-hour shift work in many countries. In Mexico, the 1917 Social Rights Declaration adhered to this position under the idea that the excessive workload above the 8-hour limit had negative effects on the health of workers; nevertheless, this statement seems to be sustained only by testimonies, anecdotal opinions and/or by the logic and common sense that then prevailed. For this reason, a literature review was carried out in search for the evidence supporting this apparently immovable length of the shift work. The globalization of the economy and the tendency towards flexibility and deregulation of current contractual relationships, are the new challenges that the 8-hour shift work is facing.