Three Indian women died of carbon monoxide poisoning on Friday in a traditional steam bath known as a "temascal" near this colonial city in southern Chiapas state, authorities reported.
The three women, aged 20, 26 and 33, entered the steam bath in the hamlet of Los Ranchos on the outskirts of San Cristobal de las Casas, but were found dead a short while later.
According to the state Attorney General's Office, the women died after carbon monoxide built up inside the low-ceilinged stone structure, apparently as a result of wood burned to heat the steam bath.
The women's bodies were found inside the structure by one of their relatives.
Many Mexican communities use the steam baths for medicinal or spiritual purposes.
Rocks are generally heated outside the structures and then carried into the baths, whose small entrances are often intentionally sealed once the steam ceremony begins.
Water and herbs are then poured over the hot rocks.
It was unclear how the deadly gas built up in the Friday case, reported AP. P.T.