Every year, hundreds of thousands of Muslims undertake the Hajj –the sacred pilgrimage to Mecca. In 2024, the pilgrimage took place in mid-June, the start of the Saudi summer.
But this year, more than 1,300 pilgrims never made it home. Lethal heat combined with humidity proved deadly.
Our new research shows the upper limits of human heat tolerance were breached for a total of 43 hours over the six days of Hajj. During these periods, heat and humidity passed beyond the point at which our bodies are able to cool down.
