About 20 others have been hospitalized in grave condition, the Investigative Committee says, adding that some are in a coma.
Methanol (also known as methyl alcohol), a light, colorless, flammable liquid, has been detected in the composition of Boyaryshnik (Hawthorn) bath lotion, health officials told TASS.
The lotion bottles were marked with warnings that they are not for internal use.
Two suspects believed to be directly involved in the distribution of the surrogate alcohol have been detained, the Investigative Committee said.
They also said that Hawthorn bath lotion was available at about 100 outlets in Irkutsk.
The injured and dead appear to be residents of the same area in Irkutsk and, according to officials, they were not drinking alcohol together, and are socially disadvantaged people aged 35 to 50.
Although poisonings with surrogate alcohol are not uncommon in Russia, the Irkutsk incident appears to be one of the most fatal in years.