An analysis of bones of children who lived as many as 400 years ago showed sky-high lead levels, which scientists now think came from their mothers' makeup.
Japan was ruled by a series of shoguns during the Edo period, from 1603 to 1867, 'LiveScience' reported.
Researchers led by Tamiji Nakashima, anatomist at the University of Occupational and Environmental Health in Kitakyushu, studied the remains of 70 samurai men, their wives and children.
They sampled the lead in rib bones, and X-rayed some of the children's long arm and leg bones looking for signs of lead poisoning. They found kids with enough lead in their systems to cause severe intellectual impairment.
Children under age 3 were the worst off, with a median level of 1,241 micrograms of lead per gram of dry bone. That's more than 120 times the level thought to cause neurological and behavioural problems today and as much as 50 times higher than levels the team found in samurai adults. Older kids' levels were lower, but still very high.
Five of the children had unusual bone enlargements, and X-rays revealed banding that only turns up in children with at least 70 micrograms of lead per deciliter of blood.
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Scientists understand that blood-lead levels of just 10 micrograms per deciliter can cause "lowered intelligence, reading and learning disabilities, impaired hearing, reduced attention span, hyperactivity, and anti-social behaviour," according to an Environmental Protection Agency website.
Nakashima and colleagues showed that samurai women had higher lead levels in their bones than samurai men did, and the researchers' suspicions settled on the women's cosmetics.
A lead-based white face powder was fashionable among the elite during the Edo period, introduced by celebrity geisha, courtesans and Kabuki actors.
The youngest children most likely picked lead up while nursing, Nakashima and his colleagues said.
Judging by the ones who didn't make it to adulthood, researchers suggest that many surviving samurai children during the Edo period probably suffered from severe intellectual impairment.