Percutaneous Penetration of Hair Dyes
February 1985
in “
Archives of dermatological research
”
TLDR Hair dyes penetrate the scalp very minimally, less than 1%.
The study evaluated the scalp penetration of 7 hair dyes (both oxidative and direct) in rhesus monkeys and humans using 14C labeled materials, with absorption measured via urine assays. Both species exhibited a similar pattern of dye penetration, with direct dyes showing slightly higher penetration. However, in neither case did the penetration exceed 1% of the applied dose.
